#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int p;

int fact(int n)
{ int i,val=0;
  for(i=5; n/i>=1; i*=5)
      val+=n/i;
  return val;
}

int main()
{ fin>>p;
  if(p==0) {fout<<1; return 0;}
  else if(p==1) {fout<<5; return 0;}
  long long s=0,d=5*p;
  int pp=0;
  long long m=-1;
  while(s<d )
        { m=(s+d)/2;
          if(fact(m)==p) d=m;
          else s=m+1;
        }

fout<<m;
    return 0;
}