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

int div2(int x) {
  int count = 0;
  while(x%2 == 0) {
    ++count; x/=2;
  }
  return count;
}

int div5(int x) {
  int count = 0;
  while(x%5 == 0) {
    ++count; x/=5;
  }
  return count;
}

int main() {
  ifstream fin("fact.in");
  ofstream fout("fact.out");
  int sum = 0, d5= 0, d2 = 0;
  int P; fin >> P;

  if(P == 0) {
    fout << "1\n";
    return 0;
  }
  
  int i;
  for(i = 5; d5 < P; i+=5) {
    d5 += div5(i);
  }
  fout << i - 5 << "\n"; 
  return 0;
}