#include <iostream>
#include <algorithm>
using namespace std;
struct Wood{
    int a=0,b=0,l=0,r=0;
};
int main(){
    long long n,FMax=-1,SMax=-1;
    cin >> n;
    Wood wood[n];
    for(int i=0;i<n;i++){
        cin >> wood[i].a >> wood[i].b;
        wood[i].l=wood[i].b,wood[i].r=wood[i].a-wood[i].b;
        if(FMax < wood[i].l or FMax < wood[i].r)
            FMax = max(wood[i].l,wood[i].r);
        else if (SMax < wood[i].l or SMax < wood[i].r)
            SMax = max(wood[i].l,wood[i].r);
    }
    cout << FMax+SMax<<endl;
}