#include<fstream>
using namespace std;

long long n,p,p2;

long long prelucreaza(int psi)
{long long result=0;
 while(psi)
  {psi=psi/5;
   result+=psi;}
 return result;  }


int main()
{
ifstream f("fact.in");
f>>p;
f.close();
long long ni, nf;
ni=1;  nf=5*p;  
int valid=0;
while(ni<=nf && valid==0)
{n=(ni+nf)/2;
p2=prelucreaza(n);
if(p2==p)
 valid=1;
else
  {if(p2>p)
      nf=n;
   if(p2<p)
      ni=n;}   
         }
ofstream g("fact.out");
n=n-n%5;
g<<n;
g.close();
return 0;    
}