#include<stdio.h>
#include<math.h>

__int64 aux,tot,cinci,p,i;

int main()
{
freopen("fact.in","r",stdin);
freopen("fact.out","w",stdout);
scanf("%I64d",&p);
i=0;
aux=p;
while(aux%5==0) aux=aux/5;
if(aux==1) {printf("-1"); return 0;}
if(p==0) {printf("1");return 0;}
while(cinci<p)
  {
  i++;
  aux=i;
  while(aux%5==0)
    {
    aux=aux/5;
    cinci++;
    }
  }
printf("%I64d",i);
return 0;
}