//https://ncode.syosetu.com/n4830bu/269/
#include <bits/stdc++.h>
using namespace std;

#include "atcoder/all"
using namespace atcoder;
using Mint = modint1000000007;

int N, S, K;

int main() {
    cin >> N >> S >> K;
    S -= N * (N - 1) / 2 * K;
    Mint maine = 0;
    if (S >= 0) {
        vector<Mint> dp(S + 1);
        dp[0] = 1;
        for (int i = 1; i <= N; i++) {
            for (int j = 0; j <= S; j++) {
                int book = j + i;
                if (book <= S)
                    dp[book] += dp[j];
                else
                    break;
            }
        }
        maine = dp[S];
    }
    cout << maine.val() << endl;
}