//
//  main.cpp
//  factorial
//
//  Created by Catalina Brinza on 11/30/13.
//  Copyright (c) 2013 Catalina Brinza. All rights reserved.
//


#include <fstream>
#define nru 1200000000
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
long long  p;

long long zerouri(long long  x)
{long long nr=0,k=5;
    while (k<=x)
    {
        nr+=x/k;
        k=k*5;
    }
    return nr;

}
void cautare(long long  a,long long  b)
{long long  m,q=-1,nr=0;
    while  (a<=b)
    { m=a+(b-a)/2;
    nr=zerouri(m);
    if (nr>p) b=m-1;
    else if (nr<p) a=m+1;
    else {
        q=m;
        b=m-1;
    }
   
}
    out<<q;
}
int  main()
{
    in>>p;
    cautare(1,nru);
    return 0;
}