#include <bits/stdc++.h>
using namespace std;

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

int d, l, m, n, maxim;
vector<int> v[1000003];

int main()
{
    in>>m>>n;
    for( int i = 1; i <= n; i++ )
    {
        in>>d>>l;
        v[d].push_back(l);
    }

    d = 0;
    for( int i = 0; i <= m; i++ )
    {
        for( unsigned int j = 0; j < v[i].size(); j++ )
        {
            if( v[i][j] != 0 && i != 0 )
                maxim = max( maxim, d + v[i][j] );

            if( d < v[i][j] )
                d = v[i][j];
        }

        d++;
    }

    out<<maxim;

    return 0;
}