#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=int(a);i<int(b);++i)
using namespace std;
typedef long long ll;
int INF = (1LL << 30) - 1;
int MOD = 1e9+7;
main(){
    int N;
    cin >> N;
    vector<ll> A(N-1);
    rep(i,0,N-1)cin >> A[i];
    ll accum = 0,ans = 0;
    rep(i,0,N-1){
        int a,b;
        cin >> a >> b;
        accum += b - a;
        ans += accum * A[i];
    }
    cout << ans << endl;
}