#include <fstream>
#include <algorithm>

using namespace std;

ifstream cin("heavymetal.in");
ofstream cout("heavymetal.out");

pair<long long,long long>v[100005];
long long n,d[100005];

long long caut(long long x,long long i){
    long long st=1,dr=i,sol=0;
    while(st<=dr){
        long long mj=(st+dr)/2;
        if(v[mj].first>x)
            dr=mj-1;
        else{
            st=mj+1;
            sol=mj;
        }
    }
    return sol;
}

int main()
{
    cin>>n;
    for(long long i=1;i<=n;i++){
        cin>>v[i].second>>v[i].first;
    }
    sort(v+1,v+n+1);
    for(long long i=1;i<=n;i++){
        d[i]=max(v[i].first-v[i].second+d[caut(v[i].second,i-1)],d[i-1]);
    }
    cout<<d[n];
    return 0;

}