#include <bits/stdc++.h>

using namespace std;

#define REP(var, n)  for (int var = 0; var < (n); var++)
#define RREP(var, n)  for (auto var = n - 1; var != static_cast<int>(-1); var--)
#define FOR(var, a, b)  for (auto var = (a); var < (b); var++)
#define RFOR(var, a, b)  for (auto var = b - 1; var != a; var--)

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef pair<int, int> pii;

#define all(c) begin(c),end(c)

#define D(x) do { std::cerr << x << " "; } while (0)
#define D2(x) do { std::cerr << #x << ": " << x << std::endl; } while (0)


template<typename T>
std::ostream &operator<<(std::ostream &out, const std::vector<T> &v) {
    if (!v.empty()) {
        out << '[';
        std::copy(v.begin(), v.end(), std::ostream_iterator<T>(out, ", "));
        out << "\b\b]";
    }
    return out;
}


template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
    return os << '(' << p.first << ',' << p.second << ')';
}


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

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

auto solve() {
    int N, K;
    cin >> N >> K;
    vi a(N);
    for (auto &&e:a) cin >> e;

    const int MOD = 1e9 + 7;

    vector<vll> dp = vector<vll>(N + 1, vll(K + 1, 0));
    dp[0][0] = 1;

    REP(i, N) {
        ll sum = 0;
        REP(j, a[i] + 1) {
            sum += dp[i][j];
            sum %= MOD;
            dp[i + 1][j] += sum;
        }

        FOR(j, a[i] + 1, K + 1) {
            sum += dp[i][j];
            sum -= dp[i][j - a[i] - 1];
            dp[i + 1][j] += sum;
        }
    }

    return dp[N][K];
}


int main() {
    cout.precision(10);
    cin.tie(0);
    ios::sync_with_stdio(false);

//    cout << (solve() ? "First" : "Second") << endl;
//    cout << (solve() ? "YES" : "NO") << endl;
    cout << solve() << endl;
//    solve();

    return 0;
}
