a[20001],i,n,s,m=1e9+7;main(j){*a=1;scanf("%d%d%d",&n,&s,&j);for(s-=~-n*n/2*j;i++<n;)for(j=i-1;j++<s;a[j]%=m)a[j]+=a[j-i];i=!printf("%d",s<0?0:a[s]);}