/******************************************************************************************
*           .--.																		  *
* ::\`--._,'.::.`._.--'/::			@author Ana M. Mihut	@course InfoArena Tryout	  *
* ::::. `  __::__ ' .:::::			@alias  LT-Kerrigan		@date   10.04.2014			  *
* ::::::-:.`'..`'.:-::::::			@link   http://infoarena.ro/problema/fact		      *
* ::::::::\ `--' /::::::::			@detail											      *
*																						  *
*******************************************************************************************/

#include <iostream>
#include <fstream>

int ChkZero(int n, int d, int divBy){
	int tmp = n / divBy;
	return ((tmp != 0) ? (ChkZero(n, d + tmp, divBy *5)) : d);
}

int main(){

	int p, mid;
	int lhs = 1;

	std::ifstream in("fact.in");
	std::ofstream out("fact.out");
	in >> p;

	int rhs = 5 * p;

	while (lhs <= rhs){
		mid = lhs + (rhs - lhs) / 2;	
		(ChkZero(mid,0,5) < p) ? (lhs = mid + 1) : (rhs = mid - 1);
	}

	(ChkZero(lhs, 0, 5) == p) ? (out << lhs) : (out << "-1");

	return 0;
}