M=10**9+7
n,s,k=gets.split.map(&:to_i)
s-=k*n*(n-1)/2
if s<0
	p 0
	exit
end

dp=Array.new(n+s+9,1)
w=1
(n-1).times{
	temp=Array.new(n+s+9,0)
	w+=1
	(s+1).times{|i|
		temp[i]=(temp[i-w]+dp[i])%M
	}
	dp=temp
}

p dp[s]