This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
#define F first
#define S second
#define PB push_back
#define PF push_front
#define MP make_pair
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;
const int maxn = 1e3 + 10;
const int mod = 1e9 + 7;
ll dp[maxn][maxn], par[maxn], a[maxn];
int main() {
int n;
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i];
par[i] = max (par[i - 1], a[i]);
}
for (int i = 1; i <= n; i++)
dp[0][i] = 1;
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) {
dp[i][j] = (j * dp[i - 1][j] + dp[i - 1][j + 1]) % mod;
}
}
ll ans = 0;
for (int i = 1; i <= n; i++) {
ans = (ans + (a[i] - 1) * dp[n - i][par[i - 1]] % mod);
}
cout << (ans + 1) % mod << endl;
}
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