#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

ifstream fin("orase.in");
ofstream fout("orase.out");

int main()
{
    int m,n,maxd=0;
    fin>>m>>n;
    vector<int>d(n),l(n);
    for(int i=0;i<n;i++){
        fin>>d[i]>>l[i];
        if(m+d[i]+l[i]>maxd) maxd=m+d[i]+l[i];
    }
    fout<<maxd;
    return 0;
}