#include <stdio.h>

int fact (int N) {
	int sum = 0, step;
	for (step = 5; step <= N; step *= 5)
		sum += N / step;
	return sum;
}

int main () {
	int N, step, i;

	freopen("fact.in", "r", stdin);
	freopen("fact.out", "w", stdout);

	scanf("%d", &N);

	for (step = 1 << 29, i = 0; step; step >>= 1)
		if (fact(i + step) < N)
			i += step;
	printf("%d\n", fact(i + 1) == N ? i + 1 : -1);
}