#include <stdio.h>

// Created: Joonas Kortesalmi (2006-11-10)
// Finnish bank transfer reference number calculator.

unsigned long long int refnum ( unsigned long long int);

int main (int argc, char *argv[]) {
	unsigned long long int inputnum;
	if (argc != 2) {
		fputs("Usage: refnum <number>\n", stderr);
		return(-1);
	} else if ( sscanf(argv[1], "%llu", &inputnum) != 1 )
	{
		fputs("Usage: refnum <number>\n", stderr);
		return(-2);
	} else {
		printf("%llu\n", refnum(inputnum));
	}

	return 0;
}

unsigned long long int refnum (unsigned long long int input) {
	unsigned int i = 0;
	unsigned long long int temp;
	unsigned int sum = 0;

	// Split the number from the end to the beginning - one number
	// at a time multiply by (7, 3, 1, 7, 3, 1, ...) and take a sum.
	for (temp = input; temp > 0; temp = temp/10) {
		switch (i++ % 3) {
			case 0:
				sum += 7 * (temp % 10);
				break;
			case 1:
				sum += 3 * (temp % 10);
				break;
			case 2:
				sum += 1 * (temp % 10);
				break;
		}
	}
	// The checksum is the distance of modulo 10 of the sum to the next
	// number divisible by 10.
	return 10*input + (10 - sum % 10) % 10;
}