#include<stdio.h>
#include<math.h>
long p;
long numar_zero(long x)
{
long c=1,e=0,p5=0;
e=1;
while(c!=0)
     {
     e=e*5;
     c=x/e;
     p5+=c;
     }
return p5;
}

long cautbin(long x)
{
long st,dr,z,n,m;
st=0;
dr=100000000;
while(st<=dr)
     {
     m=(st+dr)/2;
     n=m*5;
     z=numar_zero(n);
     if(z==p)
       return n;
     if(z<p)
       st=m+1;
     else
       dr=m-1;
     }
return -1;
}

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

scanf("%ld",&p);
if(p==0)
  {
  printf("1\n");
  return 0;
  }
long poz;

poz=cautbin(p);

printf("%ld\n",poz);
}