#include <bits/stdc++.h> using namespace std; int N; int arr[10005]; long long dp[2][10005]; const int MOD = 1000007; int solve(int n, int m, bool border){ if(n == N+1){ return 1; } if(!border && n%2 == 0 && dp[n/2][m]){ return dp[n/2][m]; } int lim = m+1; if(border){ lim = arr[n]; } long long ans = 1LL * (lim-1) * solve(n+1, m, 0); ans += solve(n+1, max(lim, m), border); ans %= MOD; if(!border && n%2 == 0){ dp[n/2][m] = ans; } return ans; } int main(){ ios::sync_with_stdio(0); cin.tie(0); cout.tie(0); cin >> N; for(int i = 1; i<=N; i++){ cin >> arr[i]; dp[1][i] = 1; } long long ans = 0; for(int i = N; i; i--){ long long m = *max_element(arr, arr+i); ans += min(1LL*arr[i]-1, m) * dp[1][m]; for(int j = 1; j<N; j++){ dp[0][j] = 1LL * j * dp[1][j] + dp[1][j+1]; dp[0][j] %= MOD; dp[1][j] = dp[0][j]; } ans %= MOD; } cout << ans+1; }