/*
infoarena
http://infoarena.devnet.ro
fact
COD: 006
*/
//5,25,125,625,3125,15625,78125,390625,1953125,9765625,48828125,244140625,1220703125,6103515605
#include <fstream.h>
#include <stdio.h>
int main()
{
	ifstream fi("fact.in");
	ofstream fo("fact.out");
	unsigned long int p,j;
	fi>>p;
	fi.close();
	unsigned long int ls=1220703125,li=5,c=1,div5=0;
	while(p!=div5)
	{
		j=(li+ls)/2;
		div5=j/5+j/25+j/125+j/625+j/3125+j/15625+j/78125+j/390625+j/1953125+j/9765625+j/48828125+j/244140625+j/1220703125;
		if(p>div5) li=j;
		if(p<div5) ls=j;
	}
	j=j-j%5;
	if(p==div5) fo<<j;
	else fo<<"-1";
	fo.close();
	return 0;
}