#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");

int power( int base, int exp);
int factorial(int n);

int main() {
	long int p, n, f, op, nr;
	in >> p;

	op=power(10, p);
		
	n = 1;
	f = factorial(n);

	while (f % op != 0) {
		f = factorial(n);
		n++;
	}
 
	out << n;
	
	return 0;

}

int power(int base, int exp) {
	int result = 1;
	for (int c = 1;c <=exp;c++) {
		result = result * base;
	}
	return result;

}


	int factorial(int n) {
		if (n > 0) { return(n * factorial(n - 1)); }
		else return 1;

	}