#include <fstream>
using namespace std;
ifstream cin("fact.in");
ofstream cout("fact.out");
long long Zero(long long n) {
  long long c=0;
  while (n>0)
  {
     c += n/5;
     n /= 5;
  }
  return c;
}

int main()
{
  int p;
  cin>>p;
  if (p==0)
  {
    cout<<1;
    return 0;
  }
     /// 10e15 este 10 la puterea a 15-a
  long long l=0, r=10e15, mid, res=-1;
  while (l<=r)
  {
    mid = l+(r-l)/2;
    long long z=Zero(mid);
    if (z<p) l=mid+1;
    else if (z>p) r=mid-1;
    else {
      r=mid-1;
      res = mid;
    }
  }
  cout<<res;
  return 0;
}