//ic210 sec4002
//hw 20
//recursive handshake

#include <iostream>

using namespace std;

int handshakes(int);
int main()
{
	int numPeople;

	//ask for number of people in room
	cout << "Enter number of people ";
	cin >> numPeople;

	//output number handshakes
	cout << "There will be " 
		<< handshakes(numPeople) 
		<< " handshakes \n";

	return 0;
	
}

//recursive function to compute number of handshakes
int handshakes(int n)
{
	//base case (simplest input)
	if (n == 1)
	{
		return 0;
	}

	//recursive case
	//assume we know the answer for n-1 
	//(that is handshakes(n-1))
	//extra person comes - shakes hand 
	//with everybody else (n-1 shakes)
	//total is (n-1) + handshake(n-1)
	return n-1 + handshakes(n-1);
}