#include<fstream.h>
#include<math.h>
#include<values.h>
ifstream in("fact.in");
ofstream out("fact.out");
long p;
long calc(int k)
{ long i=5,ret=0;
  while(floor(k/i)>0)
   {
     ret=ret+(ceil(k/i));
     i=i*5;
   }
  return ret;
}

int main()
{ long a=1,b=50000,ok,c,aux;
 in>>p;
 c=(a+b)/2;
 ok=0;
 while(a!=b)
  { c=(a+b)/2;
    if(calc(c)==p) { a=b;ok=1;}
    else
	{ aux=calc(c);
		 if (p>aux)  a=c+1;
		 else b=c-1;
	}
   }
 if(ok==1) out<<c-3;
 else out<<-1;







return 0;

 }