#include <iostream>
#include <fstream>
#include <climits>
using namespace std;
int n,k;
int det_nr_0(int n,int p);
int cb(int li,int ls,int x);
int main()
{
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    cin>>n;
    if(n==0)
    {
        cout<<1;
        return 0;
    }
    k=cb(1,1000000000,n);
    if(k==-1)
    {
        cout<<k;
        return 0;
    }
    k=k-k%5;
    cout<<k;
    return 0;
}
int det_nr_0(int n,int p)
{
    if(n>=p) return n/p+det_nr_0(n,p*5);
    else return 0;
}
int cb(int li,int ls, int x)
{
    if(li>ls) return -1;
    else
    {
        int m=(li+ls)/2;
        int nr=det_nr_0(m,5);
        if(nr==x) return m;
        else if(nr>x) return cb(li,m-1,x);
        else return cb(m+1,ls,x);
    }
}