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>
using namespace std;
int N;
int arr[10005];
int dp[5005][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];
	}
	cout << solve(1, 0, 1);
}
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