#include<iostream>
#include<fstream>
using namespace std;

int main()
{int p,putere=0,ct=0;long long n=1,i=1;
ifstream fin("fact.in");
fin>>p;
fin.close();

do
{i++;
n=i;
while(n!=0)
{
	if(n%5==0) {n=n/5;ct++;}
	else n=0;
}
putere=putere+ct;
ct=0;
}while(putere<p);
ofstream fout("fact.out");
if(putere==p) fout<<i;
else fout<<-1;
fout.close();
return 0;
}