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



using namespace std;

long p;


long find_no_of_zeros(long &mid){
  long no=0;
  long div=mid/5;
  while(div>0) {
	no=no+div;
	div=div/5;
  }	
  return no;
}


long f(long i, long j){
 long mid=(i+j)/2;
 long no=find_no_of_zeros(mid);
 if(no==p) {
  while(mid%5!=0) mid--;	
  return mid;	
 }
 if(no<p) i=mid+1;
 else if (no>p) j=mid-1;
 if(i<=j) return f(i,j);
 return -1;
}




int main(){
ifstream in; ofstream out;
in.open("fact.in"); out.open("fact.out");
out.clear();

in>>p; 
if(p==0) out<<1;
else{
 long i=1,j=p*5;
 out<<f(i,j);
}
	
return 0;	
}