#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pi pair<int, int>
#define vi vector<int>
#define vs vector<string>
#define vb vector<bool>
#define vpi vector<pi>
#define pb push_back
#define all(a) (a).begin(), (a).end()
const int mod = 1e9 + 7;
int md_inv_2 = 500000004;
int sm(int x)
{
return (((x * (x + 1)) % mod) * md_inv_2) % mod;
}
void solve()
{
int n;
cin >> n;
int h[n + 1], w[n + 1];
for (int i = 0; i < n; i++)
cin >> h[i];
for (int i = 0; i < n; i++)
{
cin >> w[i];
}
h[n] = 0;
w[n] = 0;
vpi v; // height, start_pos
v.pb({0, 0});
int ans = 0;
int pos = 1;
for (int i = 0; i <= n; i++)
{
int curr = pos;
int gwi = 0;
while (h[i] < v.back().first)
{
auto x = v.back();
v.pop_back();
int wi = (curr - x.second);
gwi += wi;
int hz = (((sm(x.first) - sm(h[i])) % mod) + mod) % mod;
int vr = (((sm(gwi) - sm(gwi - wi)) % mod) + mod) % mod;
ans = (ans + (hz * vr) % mod) % mod;
curr = x.second;
}
if (h[i] > v.back().first)
{
v.pb({h[i], pos});
}
pos += w[i];
}
cout << ans << '\n';
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(NULL);
cout.tie(NULL);
int t = 1;
// cin >> t;
while (t--)
{
solve();
}
return 0;
}
