n,s,k = map(int,input().split())
s -= n*(n-1)//2*k
if s < 0:
    print(0)
    exit()
dp = [0]*(s+1)
dp[0] = 1
MOD = 10**9+7
for i in range(1,n+1):
    for j in range(i,s+1):
        dp[j] += dp[j-i]
        dp[j] %= MOD
print(dp[-1])