#include<bits/stdc++.h>

using namespace std;

#define debug(n) cerr << #n << ':' << n << endl;
#define dline    cerr << __LINE__ << endl;

using ll = long long;
template<class T, class U> using P = pair<T,U>;
template<class T> using Heap = priority_queue<T>;
template<class T> using heaP = priority_queue<T,vector<T>,greater<T>>;
template<class T,class U> using umap = unordered_map<T,U>;
template<class T> using uset = unordered_set<T>;

template<class T>
bool ChangeMax(T&a,const T&b){
  if(a >= b) return false;
  a = b;    return true;
}

template<class T>
bool ChangeMin(T&a,const T&b){
  if(a <= b) return false;
  a = b;    return true;  
}

template<class T, size_t N, class U>
void Fill(T (&a)[N], const U&v){
    fill((U*)a,(U*)(a+N),v);
}

template<class T>
istream& operator >> (istream&is, vector<T>&v){
  for(auto&e:v)is >> e;
  return is;
}

template<long long mod>
class modint{
private:
  long long num;
  long long extgcd(long long a, long long b, long long&x, long long&y)const {
    long long d = a;
    if(b != 0){d = extgcd(b, a%b, y, x);  y -= (a/b) * x;}
    else{x = 1; y = 0;}
    return d;
  }
  long long modinverse()const{
    long long x, y;
    extgcd(num, mod, x, y);
    return (mod + x%mod)%mod;
  }
public:
  modint():num(0){}
  modint(const long long x):num((x < 0?(x+mod):x)%mod ){}
  friend modint operator+(const modint&a, const modint&b)
  {    return modint(a.num + b.num);  }
  friend modint operator-(const modint&a, const modint&b)
  {    return modint(a.num - b.num);  }
  friend modint operator*(const modint&a, const modint&b)
  {    return modint(a.num * b.num);  }
  friend modint operator/(const modint&a, const modint&b)
  {    return modint(a*b.modinverse());  }
  modint& operator+=(const modint&b)
  {    return (*this) = (*this) + b;  }
  modint& operator-=(const modint&b)
  {    return (*this) = (*this) - b;  }
  modint& operator*=(const modint&b)
  {    return (*this) = (*this) * b;  }
  modint& operator/=(const modint&b)
  {    return (*this) = (*this) / b;  }
  modint& operator++()
  {    (*this)+=1; return (*this);  }
  modint& operator--()
  {    (*this)-=1; return (*this);  }
  modint operator++(int){
    modint tmp(*this);
    ++(*this);
    return tmp;
  }
  modint operator--(int){
    modint tmp(*this);
    --(*this);
    return tmp;
  }    
  friend ostream& operator<<(ostream&os, const modint&a){
    os << a.num;
    return os;
  }
  friend istream& operator>>(istream&is, modint&a){
    long long x; is >> x;
    a = x;
    return is;
  }
};

using mint = modint<int(1e+9)+7>;

int main(){
  int n,k; cin >> n >> k;
  vector<int> v(n); cin >> v;
  vector<vector<mint>> dp(n,vector<mint>(k+1,0));

  for(int i = 0; i <= min(v[0],k); ++i) dp[0][i] = 1;
  
  for(int i = 1; i < n; ++i){

    vector<mint> sum(k+1,dp[i-1][0]);
    for(int j = 1; j < k+1; ++j) sum[j] = sum[j-1] + dp[i-1][j];

    for(int j = 0; j <= k; ++j){

      // for(int l = 0; l <= v[i]; ++l){
      // 	if(j-l < 0) break;
      // 	dp[i][j] += dp[i-1][j-l];
      // }

      if(v[i] >= j) dp[i][j] = sum[j];
      else dp[i][j] = sum[j] - sum[j-v[i]-1];
    }

    // for(int j = 0; j < k; ++j){      
    //   mint u = sum[j];
    //   mint l = (min(v[i],k) >= j ? 0 : sum[min(v[i],k) - j - 1]);
    //   dp[i][j] = u - l;
    // }
  }

  cout << dp[n-1][k] << endl;
  
  return 0;
}


Measured memory_bytes: 79472