int BinSearch(int arr[],int len,int key)                          //折半查找法（二分法）
{
	int low=0;                         //定义初始最小
	int high=len-1;                 //定义初始最大
	int mid;                            //定义中间值
	while(low<=high)
	{
		mid=(low+high)/2;              //找中间值
		if(key==arr[mid])               //判断min与key是否相等
			return mid;    
		if(key>arr[mid])             //如果key>mid  则新区间为[mid+1,high]
			low=mid+1;
		else                                       //如果key<mid  则新区间为[low,mid-1]
			high=mid-1;
	}
	return -1;                             //如果数组中无目标值key，则返回 -1 ；
}
int main()
{
	int arr2[100];
    int n;
    int i = 0;
    n = getint();
    while(i<n){
        arr2[i] = getint();
        i = i + 1;
    }
    n = BinSearch(arr2,n,9);
    putint(n);
	return 0;
}