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

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N;
    cin >> N;

    vector<ll> A(N-1);
    FOR(i, 0, N-1){
        cin >> A.at(i);
    }

    ll people = 0;
    ll sum = 0;
    FOR(i, 0, N-1){
        ll out, ride;
        cin >> out >> ride;

        people += ride;
        people -= out;

        // cost
        sum += people * A[i];
    }

    p(sum);
    
    return 0;
}