#include <iostream>
#include <cstdio>
using namespace std;
int main()
{
freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
int n,s,p,x,dr,st;
cin>>x;
st=1;
dr=5*x;
while(st<=dr)
{
    n=(st+dr)/2;
    p=5;
    s=0;
    while(n/p>0)
    {
        s=s+n/p;
        p*=5;
    }
    if(s>x)dr=n-1;
    else st=n+1;

}
if(x==0)cout<<1;
else if(s!=x)cout<<-1;
else
cout<<n;
  return 0;
}