// oooo
/*
har chi delet mikhad bebar ~
gitar o ba khodet nabar! ~
;Amoo_Hasan;
*/
#include<bits/stdc++.h>
//#pragma GCC optimize("O3,no-stack-protector,unroll-loops")
//#pragma GCC target("avx2,fma")
using namespace std;
typedef long long ll;
typedef long double ld;
#define Sz(x) int((x).size())
#define All(x) (x).begin(), (x).end()
#define wtf(x) cout<<#x <<" : " <<x <<endl
constexpr ll inf = 1e18, N = 1e6 + 10, mod = 1e9 + 7, pr = 1000696969;
int h[N], w[N];
ll bpow;
vector<int> vc;
ll poww(ll x, int y) {
ll res = 1;
for(; y; y /= 2, x = x * x % mod)
if(y & 1)
res *= x, res %= mod;
return res;
}
ll choose(ll x) {
ll res = x * (x - 1) % mod;
res *= bpow;
res %= mod;
return res;
}
int main() {
ios :: sync_with_stdio(0), cin.tie(0);
bpow = poww(2, mod - 2);
int n; cin >>n;
for(int i = 0; i < n; i++) {
cin >>h[i];
}
for(int i = 0; i < n; i++) {
cin >>w[i];
for(int j = 0; j < w[i]; j++) {
vc.push_back(h[i]);
}
}
ll ans = 0;
for(int i = 0; i < Sz(vc); i++)
for(int j = i; j < Sz(vc); j++) {
int cnt = min(vc[i], vc[j]) + 1;
for(int k = i + 1; k < j; k++) {
cnt = min(cnt, vc[k] + 1);
}
cnt = choose(cnt);
ans += cnt, ans %= mod;
}
cout<<ans;
return 0;
}
