#include<fstream>
using namespace std;
ifstream f("orase.in");
ofstream g("orase.out");
int d,l,a,b;
int main()
{
    for(f>>d>>l;f>>d>>l;a=max(a,d+l),b=max(b,l-d));
    g<<a+b;
    return 0;
}