#include<stdio.h>
int p, ok = 0, i = 0, cont = 0;
void fct(int x) {
	int c;
	if (x % 5 == 0) {
		++cont;
		c = x / 5;
		fct(c);
	}
}

int main() {
	freopen("fact.in", "r", stdin);
	freopen("fact.out", "w", stdout);
	scanf("%d", &p);
	if (p < 0) {
		printf("%d", -1);
		return 0;
	}
	while (!ok) {
		++i;
		fct(i);
		if (cont >= p)ok = 1;
	}
	
	printf("%d", i);
	
	return 0;
}