#!/usr/bin/env python3

INPUT_FILE = 'input.txt'

def main():
    left, right = [], []
    contents = open(INPUT_FILE, 'r').readlines()
    for line in contents:
        fields = line.split(' ')
        left.append(int(fields[0]))
        right.append(int(fields[-1]))
    left.sort()
    right.sort()
    diff_sum = 0
    for pair in list(zip(left, right)):
        diff_sum += abs(pair[0] - pair[1])
    print(diff_sum)


if __name__ == '__main__':
    main()