N,S,K = map(int,input().split())
S -= int(N*(N-1)/2*K)
dp = [[0]*(S+1) for _ in range(N+1)]
if S<0:
    print(0)
    exit()
if S == 0:
    print(1)
    exit()
dp[0][0] = 1
for i in range(1,N+1):
    for j in range(S+1):
        if j-i>=0:
            dp[i][j] = dp[i-1][j] + dp[i][j-i]
        else:
            dp[i][j] = dp[i-1][j]

print(dp[-1][-1]%(10**9+7))