#include <stdio.h>
#define SMAX 20000
#define MOD 1000000007

int main(void)
{
  int i, j, n, s, k, dp[SMAX+1] = {0};
  scanf("%d %d %d", &n, &s, &k);
  s -= n * (n - 1) / 2 * k;
  if (s < 0) printf("0\n");
  else {
    dp[0] = 1;
    for (i = 1; i <= n; i++) {
      for (j = i; j <= s; j++) {
        dp[j] += dp[j - i];
        dp[j] %= MOD;
      }
    }
    printf("%d\n", dp[s]);
  }
}