//cpp

#include <bits/stdc++.h>
using namespace std;  
  
int main() 
{ 
	int n;
    cin >> n;  
    long long a[n+1],b[n+1],c[n+1];  
    for (int i=1;i<=n;i++) 
	{
        cin >> a[i] >> b[i];   
		c[i] = max(b[i],a[i]-b[i]);
    }
    sort(c+1,c+1+n);
	cout << c[n] + c[n-1]; 
	
    return 0;  
}