#include <iostream>
#include <fstream>

using namespace std;

int p,ans;

int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    f>>p;
    int st=5, dr=p*5, ans=-1;
    while(st<=dr)
    {
        int m=(st+dr)/2;
        int pw=5, s=0;
        while(pw<=m)
        {
            s+=m/pw;
            pw*=5;
        }
        if(s==p)
        {
            ans=m;
            dr=m-1;
        }
        else if(s<p)
            st=m+1;
        else
            dr=m-1;
    }
    if(p==0)
        g<<1;
    else
        g<<ans;
    g<<'\n';
    f.close();
    g.close();
    return 0;
}