BE

#include <stdio.h>
typedef long long LL;
typedef unsigned long long ULL;
char s[2000200] = {0};
int main(int argc,char **argv){
    int t,days,n,i,ans,tmp;
    scanf("%d",&t);
    while(t--){
        ans = 0;tmp = 0;

        scanf("%d%s",&days,s);
        for(i = 0;i < days;i++){
            switch(s[i]){
            case '0':
                if(tmp){
                    tmp--;
                    ans++;
                }
                break;
            case '1':
                tmp++;
                break;
            case '2':
            case '3':
                ans++;
                break;
            default:
                break;
            }
        }
        printf("%d\n",ans + tmp / 2);
    }
    return 0;
}