#include<fstream>
#include<cmath>
#include<iostream>
//#include<climits>
using namespace std;

int calc(int);

int main(){
    ifstream inFile("fact.in");
    ofstream outFile;
    outFile.open("fact.out");
    long p;
    inFile>>p;
  //  int i;
  //  outFile<<LONG_MAX<<"\n";
  //  for(i=1;calc(i)<p;i++);
  if(p==0){
    outFile<<1;
    return 0;
  }
  long a=0, b=400000018;
  long k=(a+b)/2;
  long aux=calc(k);

  while(aux!=p){
    if(aux>p) b=k;
        else if(aux<p) a=k;
        else{
          break;
        }
    k=(a+b)/2;
    aux=calc(k);
    if(b-1==a && calc(k)!=p){
        outFile<<-1;
        return 0;
    }
  }

  if(k%5==0) k+=0;
    else while(k%5!=0) k--;

    outFile<<k;



}


int calc(int n){   //Calculam exponentul lui 5 in n!
    int expFive=0; //expTwo=0;
    int q=n/pow(5,1);
    for(int i=1;q>0;i++){
        expFive+=q;
        q=n/pow(5,i+1);
    }
  /*
    for(int i=1;n/pow(2,i)>0;i++) expTwo+=n/pow(2,i);
    int k;
    k=(expTwo>expFive)?expFive:expTwo;
  */
    return expFive;
}