#include <bits/stdc++.h>
#define ll long long
#define MOD 1000000007
#define endl '\n'

using namespace std;



void solve(){
    int n, k;
    cin>>n>>k;
    vector<int> arr(n);
    for(int i=0;i<n;i++)
        cin>>arr[i];

    vector<vector<ll>> dp(n+1, vector<ll>(k+1, 0));

    for(int i=1; i <= n; i++)
        dp[i][0] = 1;

    vector<ll> pre1(k+1), pre2(k+1);
    pre1[0] = 1;
    for(int j = 1; j <= k; j++){
        if(arr[0] >= j){
            dp[1][j] = 1;
        }
        pre1[j] = pre1[j-1] + dp[1][j];
    }

    for(int i = 2; i <= n; i++){
        pre2[0] = 1;
        for(int j = 1; j <= k ; j++){
            ll p = j - min(j, arr[i-1]) - 1;
            dp[i][j] = (pre1[j] - (p >= 0 ? pre1[p] : 0))%MOD;
            pre2[j] = pre2[j-1] + dp[i][j];
        }
        pre1 = pre2;
    }

    cout<<dp[n][k]<<endl;
}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    solve();

}