#include <bits/stdc++.h>
#define y second
#define x first
typedef long long ll;
using namespace std;
ll N,D[100100];
pair<int,int> A[100100];

int caut(int x){
	int st=1,dr=N;
	while(st<dr-3){
		int mid = (st+dr)/2;
		if(A[mid].y<=x) st = mid; 
		else dr = mid;
	}
	for(;st<=dr;dr--) if(A[dr].y<=x) return dr;
	return -1; 
}

int main() {
    ios_base::sync_with_stdio(0);cin.tie(0);
    ifstream cin("heavymetal.in");
    ofstream cout("heavymetal.out");
    cin >> N;
    for(int i = 1,x,y;i<=N;i++){
        cin >> x >> y;
        A[i] = make_pair(x,y);
    }
    sort(A+1,A+1+N);
    for(int i = 1;i<=N;i++){ 
		int down = caut(A[i].x);
		D[i] = A[i].y-A[i].x + (down > 0 ? D[down] : 0);
		D[i] = max(D[i],D[i-1]);
//        for(int j = 1;j<=N;j++) cout << D[j] << "\n "[j<N];
    }
    cout << D[N];
}