#include <bits/stdc++.h>
using namespace std;int v1[100010];vector<int>v[100010];int main(){int n,i,x=0,j,a,b;freopen("heavymetal.in","r",stdin);freopen("heavymetal.out","w",stdout);scanf("%d",&n);for(i=1;i<=n;i++){scanf("%d%d",&a,&b);v[b].push_back(a);x=max(x,b);}for(i=1;i<=x;i++){v1[i]=v1[i-1];for (j=0;j<v[i].size();j++)v1[i]=max(v1[i],v1[v[i][j]]+i-v[i][j]);}printf("%d",v1[x]);return 0;}