//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int N = 2e5 + 5;
const ll INF = 1e18 + 5;
const ll mod = 1e6 + 7;
const int tx[] = {1, -1, 0, 0}, ty[] = {0, 0, 1, -1};
const ll bs = 31;
#define int ll
int n, a[N], b[N], cnt, res[N];
unordered_map <int, int> dp[100005];
void rec(int cur = 1, int len = 1) {
if (len == n) {
cnt++;
for (int i = 1; i <= n; i++) {
if (a[i] != b[i])
return;
}
cout << "CH ";
cout << cnt % mod;
exit(0);
}
for (int i = 1; i <= cur + 1; i++) {
b[len + 1] = i;
rec(max(cur, i), len + 1);
b[len + 1] = 0;
}
}
int calc(int id, int mx) {
if (dp[id][mx])
return dp[id][mx];
return dp[id][mx] = (mx * calc(id - 1, mx) % mod + calc(id - 1, mx + 1)) % mod;
}
main() {
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i];
dp[i].reserve(15);
dp[0][i] = 1;
}
b[1] = 1;
int ans = 0;
int mx = 0;
for (int i = 1; i < n; i++) {
mx = max(mx, a[i]);
for (int j = 1; j < a[i + 1]; j++) {
ans = (ans + calc(n - i - 1, mx)) % mod;
}
}
cout << (ans + 1) % mod;
return 0;
}
/**
5
1 2 1 1 1
*/
