///oare mere fara normalizare?... O_o
#include <bits/stdc++.h>
using namespace std;
int n,i,dp[100010],ma,j,a,b;
vector <int>v[100010];
int main()
{
    ifstream f ("heavymetal.in");
    ofstream g ("heavymetal.out");
    f>>n;
    for(i=1; i<=n; ++i)
    {
        f>>a>>b;
        v[b].push_back(a);
        ma=max(ma,b);
    }
    for(i=1; i<=ma; ++i)
    {
        dp[i]=dp[i-1];
        for(j=0; j<v[i].size(); ++j)
            dp[i]=max(dp[i],dp[v[i][j]]+i-v[i][j]);
    }
    g<<dp[ma];
    return 0;
}