#include
      
       int fn(int * a,int n,int x){    int s=0,e=n-1;    int mid;    while(s<=e)    {        mid=(s+e)>>1;        if(a[mid] == x) return mid;        else if(a[mid] > x) e=mid-1;        else s=mid+1;    }    return -1;}int main(){    int i,a[10];    for(i=0;i<10;i++)    {        a[i]=i*2;    }    while(1)    {        scanf("%d",&i);        printf("%d\n",fn(a,10,i));    }    return 0;}