#include<iostream.h>
#include<stdio.h>
FILE *f,*g;
void main ()
{
f=fopen("fact.in","r");
g=fopen("fact.out","w");
int p;
long produs,n,x,q,i=0,max=99999999;
fscanf(f,"%d",&p);
x=1; n=0; produs=1;
for(i=1;i<=p;i++)
x*=10;          i=0;
while(produs<max&&i<1)
{
  n+=1;
  produs=produs*n;
  if(produs%x==0) i=1;
}
if(i==1) fprintf(g,"%ld",n);
else fprintf(g,"-1");
fclose(f); fclose(g);
}