#include<iostream>
using namespace std;
const int mod=1e9+7;
void candies(int n,int a[],int k){
	long long int way[n][k+1];
	for(int i=0;i<=a[0];i++)
	way[0][i]=1;
	for(int i=a[0]+1;i<k+1;i++)
	way[0][i]=0;
	for(int i=1;i<n;i++){
		way[i][0]=1;
		for(int j=1;j<k+1;j++){
			if(j<=a[i])
			way[i][j]=(way[i-1][j]+way[i][j-1])%mod;
			else
			way[i][j]=(way[i][j-1]-way[i-1][j-a[i]-1]+way[i-1][j]+mod)%mod;
		}
	}
	cout<<way[n-1][k]<<endl;
}
int main(){
	int n,k;cin>>n>>k;
	int a[n];
	for(int i=0;i<n;i++)
	cin>>a[i];
	candies(n,a,k);
}