#include <iostream>
#include <fstream>

#define MIN(a,b) ((a)<(b))?(a):(b)

const char IN[] = "fact.in", OUT[] = "fact.out";

using namespace std;

int P;

inline void read_data() {
	fscanf(fopen(IN, "r"), "%d", &P);
}

int perm_count_zeros(int P) {
	if (P == 0) return 1;
	int nr5 = 1;
	int i = 5;
	while (nr5 != P) {
		++i;
		int aux = i;
		while (aux % 5 == 0) aux /= 5, ++nr5;
	}
	return i;
}

int main() {
	read_data();
	fprintf(fopen(OUT, "w"), "%d\n", perm_count_zeros(P));
	return 0;
}