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

#define BUFFER_SIZE 1024

int main(void) {
  FILE *fp = fopen("input", "r");

  size_t lineCount = 0;

  char buffer[BUFFER_SIZE] = {0};

  // get number of lines
  size_t read = 0;

  while ((read = fread(&buffer, sizeof(char), BUFFER_SIZE, fp))) {
    for (size_t i = 0; i < read; i++) {
      if (buffer[i] == '\n') {
        lineCount++;
      }
    }
  }

  rewind(fp);

  // get data from file
  int* left = malloc((lineCount * 2 + 1) * sizeof(int));
  // haha pointer arithmetic go brrr
  int* right = left + lineCount;

  for (size_t i = 0; i < lineCount; i++) {
    int leftNum, rightNum;
    int numsGot = fscanf(fp, "%d   %d\n", &leftNum, &rightNum);

    if (numsGot == 2) {
      left[i] = leftNum;
      right[i] = rightNum;
    }
  }

  for (size_t i = 0; i < lineCount - 1; i++) {
    size_t leftMin = i;
    size_t rightMin = i;

    for (size_t j = i + 1; j < lineCount; j++) {
      if (left[j] < left[leftMin]) {
        leftMin = j;
      }

      if (right[j] < right[rightMin]) {
        rightMin = j;
      }
    }

    if (leftMin != i) {
      int temp = left[i];
      left[i] = left[leftMin];
      left[leftMin] = temp;
    }

    if (rightMin != i) {
      int temp = right[i];
      right[i] = right[rightMin];
      right[rightMin] = temp;
    }
  }

  int sum = 0;
  for (size_t i = 0; i < lineCount; i++) {
    sum += abs(left[i] - right[i]);
  }

  printf("%d\n", sum);

  free(left);
  fclose(fp);

  return 0;
}