#include<fstream.h>
int main()   
{   
ifstream f("fact.in");   
ofstream g("fact.out");   
 long long p,n,min,i,j,a,b;
 f>>p;
 int gasit=0;
 n=0;
 while(gasit==0)
 {
   n++;
   a=b=0;
   for(i=1;i<=n;i++)
   { j=i;
    while(j%2==0)
    {
     j=j/2;
     a++;
    }
    j=i;
    while(j%5==0)
    {
     j=j/5;
     b++;
    }
   }
  if(a>b)
  min=b;
  else
  min=a;
    if(min==p)
      {
        gasit=1;
         cout<<n;
     }
  }
 return 0;
}