#include <bits/stdc++.h>
using namespace std;

#define int long long

signed main(){
    int n;
    int a[110];
    cin >> n;

    for(int i = 0;i < n-1;i++){
        cin >> a[i];
    }

    int now = 0;
    int b, c;
    cin >> b >> c;
    now += c; 
    int ans = 0;

    for(int i = 0;i < n-1;i++){
        ans += now * a[i];
        cin >> b >> c;
        now += -b + c;
    }

    cout << ans << endl;
    return 0;
}