import sys


def input(): return sys.stdin.readline().rstrip('\n')


def main():
    MOD = 10**9+7
    n, s, k = map(int, input().split())
    s -= n*(n-1)//2 * k
    if s < 0:
        print(0)
        return

    dp = [1] + [0]*s

    for i in range(1, n+1):
        for j in range(i, s+1):
            dp[j] += dp[j-i]
            if dp[j] >= MOD:
                dp[j] -= MOD

    print(dp[-1])


if __name__ == '__main__':
    main()