#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int main()
{
  int p,n,st,k,dr,s=0,mij,x,sol=1;
  fin>>p;
  dr=p*5;
  st=1;
  while(st<=dr)
  {
      mij=(st+dr)/2;s=0;
      x=mij;k=5;
      while(k<=x)
      {
          s=s+x/k;
          k=k*5;
      }
      if(s==p){sol=mij;dr=mij-1;}
      else if(s<p){st=mij+1;}
      else dr=mij-1;


  }fout<<sol;

    return 0;
}