Combination Program using functions in c++

#include<iostream>
using namespace std;



int main ()
{
int x, y, z, m, n, r;
int o;
int fac(int n);
cout<<"number of man:";
cin>>n;
x= fac(n);
cout<<"number of thing:";
    cin>>r;
y= fac(r);
z= n-r;
    o = fac(z);
    m = o*y;
    n = x/m;
    cout<<"total possible combination among them:"<<n;
    return 0;
}

int fac(int n)
{
    int a=1;
    for(int i=1; i<=n; i++)
    {
a= a*i;
    }
return a;
}
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output: