P = 10 ** 9 + 7

N, S, K = map(int, input().split())

S -= K * N * (N - 1) // 2

if S < 0:
    print(0)
    
else:
    dp = [0] * (S + 1)
    
    dp[0] = 1
    
    for i in range(N, 1, -1):
        for j in range(i, S + 1):
            dp[j] += dp[j - i]
            
    print(sum(dp))