#include<stdio.h>

long t,p,i;
bool ok;

int main()

{

 freopen("fact.in","r",stdin);
 freopen("fact.out","w",stdout);

 scanf("%ld",&p);

 if(p==0)

  printf("1");

 for(i=5;(ok != true)||(i<=100000000);i+=5)

 {

  t = (long)(i/5) + (long)(i/25) + (long)(i/125) + (long)(i/625) +(long)(i/3125) + (long)(i/15625) + (long)(i/78125) + (long)(i/390625) + (long)(i/1953125) + (long)(i/9765625) + (long)(i/48828125) + (long)(i/244140625);

  if(t==p)

  {

   ok = true;
   printf("%ld",t);

  }

 }

 if(ok == false)

 printf("-1");

 return 0;


}