#include<iostream>
#include<cmath>
using namespace std;
double funy(double n)
{
if(n==1)
return 1;
else
return (funy(n-1)*n);
}
void main()
{
double m,n,k,a;
cout<<"请输入m、n(n>=m)的值:"<<endl;
cin>>m>>n;
if(m>n)
{
cout<<"请重新输入m、n(n>=m)的值:"<<endl;
cin>>m>>n;
}
if(n==m)
k=1;
else
{
a=funy(n-m);
m=funy(m);
n=funy(n);
k=n/(m*a);
}
cout<<"k="<<k<<endl;
}