#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<ll>>;
struct fenwick_tree {
	ll n;
	vll bit;
	fenwick_tree(ll num) :bit(num + 1, 0) { n = num; }

	void add(ll i, ll w) {
		for (ll x = i+1; x <= n; x += x & -x) {
			bit[x-1] += w;
		}
	}

	ll sum(ll i) {
		ll ret = 0;
		for (ll x = i+1; x > 0; x -= x & -x) {
			ret += bit[x-1];
		}
		return ret;
	}

	ll sum(ll L, ll R) {
		return sum(R) - sum(L);
	}


};
ll TE(vll A) {
	ll res = 0;
	ll N = A.size();
	fenwick_tree fw(N);
	rep(i, N) {
		res += i - fw.sum(A[i]-1);
		fw.add(A[i], 1);
	}
	return res;
}

int main() {

    ll N,K;
    cin>>N>>K;
    ll mod;
    rep(i,N)cin>>mod;
    mod=1e9+7;
    vector<vll> DP(N+1,vll(K+1,0));
    rep(i,K+1){
        DP[0][i]=1;
    }
    DP[0][0]=1;
    rep(i,N)rep(j,K+1){
        DP[i+1][j]=(j-1>=0?DP[i+1][j-1]:0)+DP[i][j]-(j-i-1>=0?DP[i][j-i-1]:0);
        DP[i+1][j]%=mod;
    }
    cout<<(DP[N][K]+mod)%mod<<endl;



}