#include <stdio.h>
#include <vector>
#include <math.h>

#define PLIMIT	100000000

int binarySearch(std::vector<int> &v, int low, int high, int x) {

	if (low > high)
		return -1;

	int mid = low + (high - low) / 2;
	if (v[mid] <= x && x < v[mid + 1])
		return mid;

	if (x < v[mid])
		return binarySearch(v, low, mid - 1, x);
	return binarySearch(v, mid + 1, high, x);
}

int exactBinarySearch(std::vector<int> &v, int low, int high, int x) {

	if (low > high)
		return -1;

	int mid = low + (high - low) / 2;
	if (v[mid] == x)
		return mid;

	if (x < v[mid])
		return exactBinarySearch(v, low, mid - 1, x);
	return exactBinarySearch(v, mid + 1, high, x);
}

int factorial(std::vector<int> &n_fives, int P) {

	int N = 0, size = n_fives.size(), current, cP, exponent;

	while (P != 0) {
		current = binarySearch(n_fives, 0, size, P);

		if (current < 0)
			return current;

		exponent = (int) pow(5, current);
		cP = P / n_fives[current];
		N += exponent * cP;
		P %= n_fives[current];

	}

	return N;
}

int main(void) {
	int N, P, i = 1, plusFives, size;
	FILE *fin = fopen("fact.in", "r");
	fscanf(fin, "%d", &P);
	fclose(fin);

	std::vector<int> numberOf5s;

	numberOf5s.push_back(0);

	while (true) {
		numberOf5s.push_back(5 * numberOf5s[i - 1] + 1);
		if (numberOf5s[i] > PLIMIT)
			break;
		i++;
	}

	/*std::vector<int> notPossible;

	notPossible.push_back(5);

	for (int k = 50; k <= 10 * P; k += 25) {
		printf("Pentru %d:\n", k);
		notPossible.push_back(notPossible[notPossible.size() - 1] + 6);
		printf("\tel = %d\n", notPossible[notPossible.size() - 1]);
		N = k / 25;

		while (N % 5 == 0) {
			notPossible.push_back(notPossible[notPossible.size() - 1] + 1);
			printf("\t\tel = %d\n", notPossible[notPossible.size() - 1]);
			N /= 5;
		}
	}


	if (exactBinarySearch(notPossible, 0, notPossible.size() - 1, P) > -1)
		N = -1;
	else*/
	N = factorial(numberOf5s, P);

	FILE *fout = fopen("fact.out", "w");
	fprintf(fout, "%d", N);
	fclose(fout);

	return 0;
}