#include <cstdio>
#include <algorithm>
using namespace std;
#define ll long long
int main(){
	ll n, k, a, mod = 1000000007;
	scanf("%lld %lld", &n, &k);
	ll dp[k + 1], p[k + 2];
	for (ll i = 0; i < n; i++){
		scanf("%lld", &a);
		fill(dp, dp + k + 1, 0);
		if (i == 0) for (ll j = 0; j <= a; j++) dp[j] = 1;
		else for (ll j = 0; j <= k; j++) dp[j] = (p[j + 1] - p[max(0ll, j - a)] + mod) % mod;
		p[0] = 0;
		for (ll j = 0; j <= k; j++) p[j + 1] = (p[j] + dp[j]) % mod;
	}
	printf("%lld\n", dp[k]);
}