#include<bits/stdc++.h>
using namespace std;
int n;
long long a[200001],b[200001],c[400002];
int sum=0;
int main(){
    //freopen("bamboo.in","r",stdin);
    //freopen("bamboo.out","w",stdout);
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>a[i]>>b[i];
    }
    for(int i=0;i<n;i++){
        c[++sum]=b[i];
        c[++sum]=a[i]-b[i];
    }
    sort(c,c+sum);
    int x=c[sum]+c[sum-1];
    cout<<x<<endl;
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}