#include <iostream>
#include <fstream>
using namespace std;

int count5(int k){
  int cnt = 0;
  while(k){
    cnt += k / 5;
    k /= 5;
  }
  return cnt;
}

int main(){
  int p , fail = -1;
  ifstream fin("fact.in");
  ofstream fout("fact.out");
  fin >> p; fin.close();
  int left = 1,right = 100000000000;
  while (left <= right){
      int middle = (left + right) / 2;
      if (count5(middle) < p) left = middle + 1;
          else right = middle - 1;
  }
  if (count5(left) == p) fout << left;
     else fout << fail;
  fout.close();
  return 0;
}