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

int main()
{
 unsigned long long i,p,aux0,ok,n,aux,fact;
fact=1;
i=1;
ok=1;
in>>p;
cout<<"p=";
cin>>p;
while(ok==1)
{
    fact=fact*i;
    i=i+1;
    aux=fact;
    aux0=0;
    while(aux%10==0)
    {
        aux=aux/10;
        aux0=aux0+1;
    }
    if(aux0==p)
        ok=0;
        n=i-1;
}
if(aux0==p)
{
    cout<<n;
    out<<n;
}
    else
        cout<<"-1";

    return 0;
}