n,s,k = map(int, input().split())
s -= (n*(n-1)//2)*k
dp = [ [1]*(s+1) for _ in range(n+1) ]

for i in range(2, n+1):
  for j in range(s+1):
    if j >= i:
      dp[i][j] = dp[i-1][j] + dp[i][j-i]
    else:
      dp[i][j] = dp[i-1][j]

print(dp[-1][-1])