自己看

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n;
ll a[110];
ll x;
int main(){
	//freopen(".in","r",stdin);
	//freopen(".out","w",stdout);
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	std::cout.tie(nullptr);
	cin>>n;
    for(ll i=1;i<=n;i++) cin>>a[i];
    cin>>x;
    ll l=1,r=n;
    while(l<=r){
        ll mid=l+r>>1;
        if(a[mid]==x){
            cout<<mid<<endl;
            return 0;
        }else{
            if(a[mid]>x){
                r=mid-1;
            }else{
                l=mid+1;
            }
        }
    }
    cout<<-1<<endl;
	//fclose(stdin);
	//fclose(stdout);
	return 0;
}
//coder::by::M91