#include <iostream>
using namespace std;
int factorial(int x)
{
int i,fact;
fact=1;
for(i=1;i<=x;i++)
{
fact*=i;
}
return fact;
}
int strangeri(int x)
{
int k;
k=factorial(x)/(factorial(2)*factorial(x-2));
return k;
}
int main()
{
int n;
cout << "Persoane: "; cin >> n;
cout << "Strangeri: " << strangeri(n);
return 0;
}