#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define fi first
#define se second
#define rep(i,s,n) for(int i = s;i<n;i++)
#define rrep(i,s,n) for(int i = (n)-1;i>=(s);i--)
#define all(v) (v).begin(),(v).end()
#define chmin(a,b) a=min((a),(b))
#define chmax(a,b) a=max((a),(b))
#define endl '\n'
#define IOS() ios_base::sync_with_stdio(0);cin.tie(0)
typedef long long ll;
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
const ll MOD=1000000007,INF=1e18;

int N;

signed main() {
    IOS();
    cin>>N;
    vint a(N-1),s(N,0);
    rep(i,0,N-1){
        cin>>a[i];
    }
    
    int ans=0,cnt=0;
    rep(i,0,N){
        int b,c;
        cin>>b>>c;
        cnt+=c;
        cnt-=b;
        ans+=cnt*a[i];
    }
    cout<<ans<<endl;
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    return 0;
}