Problem:
Score : 100 points

Problem Statement

Snuke has a favorite restaurant.

The price of any meal served at the restaurant is 800 yen (the currency of Japan), and each time a customer orders 15 meals, the restaurant pays 200 yen back to the customer.

So far, Snuke has ordered N meals at the restaurant.
Let the amount of money Snuke has paid to the restaurant be x yen, and let the amount of money the restaurant has paid back to Snuke be y yen.
Find x-y.

Constraints

1 ≤ N ≤ 100

Input

The input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

20

Sample Output 1

15800

So far, Snuke has paid 16000 yen, and the restaurant has paid back 200 yen. Thus, the answer is 15800.

Sample Input 2

60

Sample Output 2

47200

Snuke has paid 48000 yen for 60 meals, and the restaurant has paid back 800 yen.

Solution in C (Clang 3.8.0) (judge verdict: Wrong Answer)

#include <stdio.h>

int main()
{
	unsigned long long int n;
	unsigned long long int m;
	scanf( "%llu %llu", &n, &m );
	
	unsigned long long int ans = 0ULL;
	
	unsigned long long int scc_n = (unsigned long long int)( n / 2ULL );
	unsigned long long int r_c_n = (unsigned long long int)( n % 2ULL );
	
	unsigned long long int scc_m = (unsigned long long int)( m / 4ULL );
	unsigned long long int r_c_m = (unsigned long long int)( m % 4ULL );
	
	unsigned long long int r_scc = (unsigned long long int)( r_c_n * 2ULL + r_c_m );
	r_scc = (unsigned long long int)( r_scc / 4ULL );
	
	ans = (unsigned long long int)( scc_n + scc_m + r_scc );
	
	printf( "%llu\n", ans );
	
	return 0;
}