#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <math.h>

using ll = long long;
using namespace std;

const int MOD = 1e9+7;

int main() {
    int n, ans = 0, capa = 0;
    cin >> n;
    vector<int> a(n-1), b(n), c(n);
    for(int i = 0; i < n-1; i++)
    {
        cin >> a[i];
    }
    for(int i = 0; i < n; i++)
    {
        cin >> b[i] >> c[i];
    }
    for(int i = 0; i < n-1; i++)
    {
        capa += c[i] - b[i];
        ans += capa * a[i];
    }
    cout << ans << endl;
    return 0;
}