#include <fstream>
using namespace std;
ifstream f("orase.in");
ofstream g("orase.out");
int x,y,difmax,summax;
int main()
{
    f>>x>>y;
    while(f>>x>>y)
    {
        if(x+y>summax) summax=x+y;
        if(y-x>difmax) difmax=y-x;
    }
    g<<summax+difmax;
    return 0;
}