#include<bits/stdc++.h>
using namespace std;
ifstream f("heavymetal.in");
ofstream g("heavymetal.out");
int n,i,j,x,y,t,dp[1<<17];
vector<int>v[1<<17];
int main()
{
    for(f>>n;i<n;++i)
    {
        f>>x>>y;
        v[y].push_back(x);
        t=max(t,y);
    }
    for(i=1;i<=t;++i)
        for(dp[i]=dp[i-1],j=0;j<v[i].size();++j)
            dp[i]=max(dp[i],dp[v[i][j]]+i-v[i][j]);
    g<<dp[t];
    return 0;
}