#include <stdio.h>
int main () {

    int n,i,a,four=0,three=0,two=0,one=0,cnt1,cnt2,cnt3,sum,cnt4,rem,sum1;
    scanf("%d",&n);
    for(i=0; i<n; i++){
        scanf("%d",&a);
        if(a==1) one++;
        if(a==2) two++;
        if(a==3) three++;
        if(a==4) four++;
    }
                if((one>0 && two>0 && three==0 && four>0)){
                    if(two%2==0){
                        cnt1=two/2;
                        rem=0;
                }
                    else if(two%2!=0){
                        cnt1=two/2;
                        rem=2;
                }
                sum1=rem+one;
                if(sum1%4==0) cnt2=sum/4;
                else cnt2=(sum1/4)+1;

                sum=cnt1+cnt2+four;
                printf("%d\n",sum);
                }
            else if(one>0 && two==0 && three>0 && four>0){
                if(one==three){
                    cnt1=(one+three)/2;
                }
                if(one>three){
                    rem=one-three;
                    if(rem%4==0) cnt1=rem/4;
                    else if (rem<4) cnt1=1;
                    else if (rem>4) cnt1= (rem/4)+1;

                }
                if(one<three){
                    rem=three-one;
                    cnt1=rem+one;
                }
                sum=four+cnt1;
                printf("%d\n",sum);
            }
            else if(one==0 && two>0 && three>0 && four>0){
                if(two%2==0) cnt1=two/2;
                else cnt1= (two/2)+1;
                sum=three+four+cnt1;
                printf("%d\n",sum);
            }
            else if(one>0 && two>0 && three>0 && four==0){
                if(one==three){
                    cnt1=(one+three)/2;
                    if(two%2==0) cnt2 =two/2;
                    else cnt2=(two/2)+1;
                    sum= cnt1+cnt2;
                    printf("%d\n",sum);
                    return 0;
                }
                if(one>three){
                    rem=one-three;
                    cnt1=three;
                    if(two%2==0) cnt2 =two/2;
                    else {
                        sum1= (two*2)+rem;
                        if(sum1%4==0) cnt2=sum1/4;
                        else cnt2= (sum1/4)+1;
                    }
                    sum= cnt1+cnt2;
                    printf("%d\n",sum);
                    return 0;
                }
               if(one<three){
                    rem=three-one;
                    cnt1= rem+ one;
                     if(two%2==0) cnt2=two/2;
                        else cnt2= (two/2)+1;
                    sum= cnt1+cnt2;
                    printf("%d\n",sum);
                    return 0;
                }
            }
            else if (one==0 && two==0 && three!=0 && four!=0){
                sum=three+four;
                printf("%d\n",sum);
                    return 0;
            }
            else if (one!=0 && two==0 && three==0 && four!=0){
                if(one%4==0) cnt1= one/4;
                else cnt1= (one/a)+1;

                sum= cnt1+four;
                printf("%d\n",sum);
                    return 0;
            }
            else if (one!=0 && two!=0 && three==0 && four==0){
                sum1=(two*2)+one;
                if(sum1%4==0) cnt1=sum1/4;
                else cnt1= (sum1/4)+1;
                sum=cnt1;
                printf("%d\n",sum);
                    return 0;
            }
            else if(one==0 && two!=0 && three!=0 && four==0){
                sum= two+three;
                printf("%d\n",sum);
                    return 0;
            }
            else if (one!=0 && two==0 && three!=0 && four==0){
                    if(one==three){
                    cnt1=(one+three)/2;
                }
                if(one>three){
                    rem=one-three;
                    if(rem%4==0) cnt1=rem/4;
                    else if (rem<4) cnt1=1;
                    else if (rem>4) cnt1= (rem/4)+1;

                }
                if(one<three){
                    rem=three-one;
                    cnt1=rem+one;

                }
                    printf("%d\n",cnt1);
                    return 0;
            }
            else if (one==0 && two==0 && three==0 && four!=0){
                    printf("%d\n",four);
                    return 0;
            }
            else if (one==0 && two!=0 && three==0 && four==0){
                    if(two%2==0) sum= two/2;
                    else sum=(two/2)+1;
                    printf("%d\n",sum);
                    return 0;
            }
            else if (one!=0 && two==0 && three==0 && four==0){
                if(one%4==0) sum= one/4;
                else sum=(one/4)+1;
                printf("%d\n",sum);
                    return 0;
            }
            else if (one==0 && two==0 && three!=0 && four==0){
                printf("%d\n",three);
                    return 0;
            }
            else if(one!=0 && two!=0 && three!=0 && four!=0){
                if(one==three){
                    cnt1=(one+three)/2;
                    if(two%2==0) cnt2 =two/2;
                    else cnt2=(two/2)+1;
                    sum= cnt1+cnt2+four;
                    printf("%d\n",sum);
                    return 0;
                }
                if(one>three){
                    rem=one-three;
                    cnt1=three;
                    if(two%2==0) cnt2 =two/2;
                    else {
                        sum1= (two*2)+rem;
                        if(sum1%4==0) cnt2=sum1/4;
                        else cnt2= (sum1/4)+1;
                    }
                    sum= cnt1+cnt2+four;
                    printf("%d\n",sum);
                    return 0;
                    }
                if(one<three){
                        rem=three-one;
                        cnt1=rem+one;
                        if(two%2==0) cnt2=two/2;
                        else cnt2= (two/2)+1;
                        sum= cnt1+cnt2+four;
                        printf("%d\n",sum);
                        return 0;
                    }
            }

}