Initializing a variable

I'm trying to make a program that takes three scores from the user then averages them, I think I almost have it down except that Im getting an error about not initializing one of my variables but I don't know where the problem lies.

 //Game Score Average
//Program that gets three game scores from user and displays the average

#include <iostream>

using std::cout;
using std::cin;
using std::endl;

int main()
{
	int score1, score2, score3;
	int score4 = score1 + score2 + score3;

	//First score input
	cout << "Enter a number:";
	cin >> score1;

	//Second score input
	cout << "Enter a second number:";
	cin >> score2;
	
	//Third Score input
	cout << "Enter a third number:";
	cin >> score3;

	//Three scores averaged
	cout <<  score4;
	cout << "\n";

	system ("pause");
	return 0;
}