代码：

#include<bits/stdc++.h>
using namespace std;
long long int a[1000000001],b[1000000001];
int main(){
    int n;
    cin >> n;
    for (int i = 1; i <= n; ++i) {
        cin >> a[i] >> b[i];
    }
    int k = 0;
    for (int i = 1; i <= n - 1; ++i) {
        int d = a[i + 1] - a[i];
        if (b[i] >= d) continue;
        k = max(k, d - b[i]);
    }
    cout << k << endl;
	return 0;
}