#include <bits/stdc++.h>
using namespace std;

int n, s, k;

void input()
{
    cin >> n >> s >> k;
}

const int S = 20010;
const int mod = 1000000007;

int dp[S];

int solve()
{
    s -= n * (n - 1) / 2 * k;
    if (s < 0) return 0;

    dp[0] = 1;
    for (int i = 0; i < n; ++i) {
        const int t = n - i;
        for (int j = t; j <= s; ++j) {
            dp[j] += dp[j - t];
            if (dp[j] >= mod) dp[j] -= mod;
        }
    }
    return dp[s];
}

int main()
{
    input();
    cout << solve() << endl;
}