#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include<fstream> 
#include<cstdio> 


using namespace std;

int main(){
    
    ifstream f ("fact.in");
    ofstream g ("fact.out");
    long n, i, j;
    long coefSolutie;
    long solutie;
    
    f >> n;
    if (n == 0){
       g << 1;
       f.close();
       g.close();
       return 0;
       }
       
    i = 0;
    while (n > 0){
          if (n >= 20){
                i += 5;
                n -= 6;
                while (j/5 > 25){
                if (j%5 == 0){
                   n--;
                   j /=5;
                }
                else
                    break;
                     
          }
             }
          else{
          i++;
          j = i;
          n--;
          while (j != 0){
                if (j%5 == 0){
                   n--;
                   j /=5;
                }
                else
                    break;
                     
          }
          }
    }               
    if (n == 0)
       solutie = 5 * i;
    else
        solutie = -1;
    g << solutie;
    
    f.close();
    g.close();
}