#include<stdio.h>
#define DIM 50001
int n,m,a,b,s[DIM],max;
int main ()
{
    freopen ("orase.in","r",stdin);
    freopen ("orase.out","w",stdout);
    int i;
    scanf("%d%d",&m,&n);
    for(i=1;i<=n;++i)
    {
                     scanf("%d%d",&a,&b);
                     s[i]=a+b;
                     if(max<s[i])
                     max=s[i];
                     }
                     printf("%d",max+m);
                     return 0;
    }