#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000


int main(void)
{
    cin.tie(0);
    ios::sync_with_stdio(false);
	int n; cin >> n;
	int a[n];
	a[0] = 0;
	rep(i, n - 1) cin >> a[i + 1];
	int ans = 0;
	int num = 0;
	rep(i, n) {
		ans += a[i] * num;
		int b, c;
		cin >> b >> c;
		num -= b;
		num += c;
	}
	cout << ans << endl;

    return 0;
}