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<iostream>
#define mod 1000007
using namespace std;
int n, t, i, j, k;
int d[2][10005], v[10005], maxim[10005];
int main(){
    cin>> n;
    for(i = 1; i <= n; i++){
        cin>> v[i];
        maxim[i] = max(maxim[i - 1], v[i]);
    }
    for(i = 1; i <= n; i++){
        d[0][i] = 1;
    }
    t = 1;
    for(i = n; i >= 2; i--){
        for(j = 1; j < i; j++){
            d[t][j] = d[1 - t][j + 1];
            d[t][j] = (d[t][j] + j * 1LL * d[1 - t][j]) % mod;
        }
        for(j = 1; j < v[i]; j++){
            k = (k + d[1 - t][ maxim[i - 1] ]) % mod;
        }
        t = 1 - t;
    }
    k = (1 + k) % mod;
    cout<< k;
}
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