#include <stdio.h>

int five_factors(int n) {
	long result = 0;
	while (n > 1) {
		result++;
		n /= 5;
	}
	return result;
}

int main() {
	freopen("flip.in", "rt", stdin);
	freopen("flip.out", "wt", stdout);
	long p, n = 0, factors[11] = {0}, actual = 0, top = 0;
	
	while (actual < p) {
		n += 5;
		factors[top]++;
		if(factors[top] == 0)
			top++;
		actual += top;
	}
	
	if (actual > p)
		return -1;
	else
		return n;
}