#include<iostream>
using namespace std;
int a[105];
int bs(int left, int right, int x) {
	int mid = (left + right) / 2;
	if(x<a[mid]){
		return bs(left,mid-1,x);
	}else if(x>a[mid]){
		return bs(mid+1,right,x);
	}else{
		return mid;
	}
}
int main() {
	int n,x;
	cin >> n;
	for(int i=0;i<n;i++){
		cin>>a[i];
	}
	cin>>x;
	cout<<bs(0,n,x);
}

请问如何判断是否有这个数并且输出-1