# include <iostream>
# include <string>
# include <math.h>
# include <fstream>

using namespace std;

int main(){

	int z,n,p,kmax,d,ok,i;
	
	ifstream f("fact.in");
	ofstream g("fact.out");
	
	
	f>>p;
	n=1;
	while(ok){
	kmax=log(n)/log(5);
	z=0;
	for(i=1;i<=kmax;i++)z+=n/pow(5,i);
		if(z==p){ok=0;d=n;}
		n++;
	}
	if(z==p)g<<d;
	else g<<-1;
	return 0;
	f.close();
	g.close();
}