#include <stdio.h>



const int MAXM=100000;

int C,M;

int x[MAXM],l[MAXM];

int answer;

int right[MAXM];

int f[MAXM];



void quick_sort(int L,int R)

{

     int x_mid=x[(L+R)>>1];

     int l_mid=l[(L+R)>>1];

     int i=L,j=R;

     while (i<=j)

     {

           while ((x[i]<x_mid)||(x[i]==x_mid&&x[i]+l[i]>x_mid+l_mid)) i++;

           while ((x[j]>x_mid)||(x[j]==x_mid&&x[j]+l[j]<x_mid+l_mid)) j–;

           if (i<=j)

           {

              int swap;

              swap=x[i];

              x[i]=x[j];

              x[j]=swap;

              swap=l[i];

              l[i]=l[j];

              l[j]=swap;

              i++;

              j–;

           }

     }

     if (L<j) quick_sort(L,j);

     if (i<R) quick_sort(i,R);

}



int main()

{

    freopen(“corral.in”,“r”,stdin);

    freopen(“corral.out”,“w”,stdout);

    scanf(“%d %d\n”,&C,&M);

    for (int i=0;i<M;i++)

        scanf(“%d %d\n”,&x[i],&l[i]);



    quick_sort(0,M-1);



    for (int i=0,j=0;j<M;)

    {

        x[i]=x[j];

        l[i]=l[j];

        j++;

        while ((x[i]+l[i]>=x[j]+l[j])&&(j<M)) j++;

        i++;

        if (j>=M) M=i;

    }



    //for (int i=0;i<M;i++)

    //    printf(“%d %d\n”,x[i],x[i]+l[i]);



    for (int i=M-1,j=M-1;i>=0;i–)

    {

        while ((x[j]>x[i]+l[i])&&(j>=0)) j–;

        right[i]=j;

    }



    answer=MAXM;

    for (int begin=M-1;;begin–)

    {

        if (x[begin]+l[begin]<C) break;

        int X=x[begin]+l[begin]-C;

        int L=x[begin]-X;

        if (L<=0)

        {

           answer=1;

           break;

        }



        //printf(“begin:%d\n”,begin);

        //printf(“X=%d X+L=%d\n”,X,X+L);

        f[begin]=1;

        for (int i=begin-1,j=begin;i>=0;i–)

        {

            //while (x[j]>x[i]+l[i]) j–;

            //printf(“i%d j%d\n”,i,j);

            f[i]=f[right[i]]+1;

            //f[i]=f[j];

            //for (int k=j;k>i;k–)

            //    if (f[i]>f[k])

            //       f[i]=f[k];

            //f[i]++;



            if (x[i]<=X)

            {

               if (answer>f[i]) answer=f[i];

               //printf(“begin:%d f[%d]=%d\n”,begin,i,f[i]);

               break;

            }

        }

    }



    printf(“%d\n”,answer);



    fclose(stdin);

    fclose(stdout);

    return 0;

}