#include<fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p;
bool check(long long val)
{
  long long s=0,x,f=5;
  x=val;
  while(x/f!=0)
  {
      s=s+x/f;
      f=f*5;
  }
  if(s>=p)
    return true;
  else
    return false;
}
long long cautbin()
{
    long long l=1,r=10000000000000,sol,mid;
    while(l<=r)
    {
        mid=(l+r)/2;
        if(check(mid)==1)
        {
            sol=mid;
            r=mid-1;
        }
        else
            l=mid+1;
    }
    return sol;
}
int main()
{
fin>>p;
if(p!=0)
fout<<cautbin();
else
    fout<<1;
}