#include <iostream>  
#include <algorithm>  
#define int long long  
using namespace std;  
  
const int N=1e5+5;  
int n,a[N],b[N],c[N];  
signed main() { 
    cin>>n;  
    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;  
}