#include <stdlib.h>
#include <stdio.h>

#define LINES 1000

int compare(const void *a, const void *b);

int main()
{
	// populate arrays from file
	FILE *input;
	input = fopen("./input", "r");
	unsigned int left[LINES];
	unsigned int right[LINES];

	for (int i = 0; i < LINES; i++) {
		fscanf(input, "%d", &left[i]);
		// printf("%d left: %d	", i, left[i]);
		fscanf(input, "%d", &right[i]);
		// printf("%d right: %d\n", i, right[i]);
	}
	/*
	for (int i = 0; i < LINES; i++) {
		printf("%d left: %d	", i, left[i]);
		printf("%d right: %d\n", i, right[i]);
	}
	*/

	// check how many times left[i] is in right[]. multiply left[i] by this.
	// then sum it
	unsigned long int sum = 0;
	for (int i = 0; i < LINES; i++) {
		int numRight = 0;
		for (int j = 0; j < LINES; j++) {
			numRight += left[i] == right[j];
		}
		sum += left[i] * numRight;
	}
	
	printf("sum: %d\n", sum);
}

int compare(const void *a, const void *b)
{
	int int_a = * ((int*) a);
	int int_b = * ((int*) b);
	
	if (int_a == int_b) return 0;
	else if (int_a < int_b) return -1;
	else return 1;
}