import std.stdio, std.string, std.conv;
import std.range, std.algorithm, std.array, std.typecons, std.container;
import std.math, std.numeric, core.bitop;

enum inf = 10L^^15;
enum mod = 10L ^^ 9 + 7;

void main() {
    int n, k;
    scan(n, k);
    auto a = readln.split.to!(int[]);

    auto dp = new long[][](n + 1, k + 1);
    dp[0][0] = 1;

    foreach (i ; 1 .. n + 1) {
        foreach (j ; 0 .. k + 1) {
            dp[i][j] = dp[i-1][j];
            if (j > 0) {
                dp[i][j] += dp[i][j-1];
                dp[i][j] %= mod;
            }
            if (j - a[i-1] - 1 >= 0) {
                dp[i][j] += mod - dp[i-1][j-a[i-1]-1];
                dp[i][j] %= mod;
            }
        }
    }

    debug {
        writefln("%(%s\n%)", dp);
    }

    auto ans = dp[n][k];

    writeln(ans);
}







void scan(T...)(ref T args) {
    import std.stdio : readln;
    import std.algorithm : splitter;
    import std.conv : to;
    import std.range.primitives;

    auto line = readln().splitter();
    foreach (ref arg; args) {
        arg = line.front.to!(typeof(arg));
        line.popFront();
    }
    assert(line.empty);
}


void fillAll(R, T)(ref R arr, T value) {
    static if (is(typeof(arr[] = value))) {
        arr[] = value;
    }
    else {
        foreach (ref e; arr) {
            fillAll(e, value);
        }
    }
}