#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
#define mem(a, b) memset(a, b, sizeof(a))
#define rep(i, a, b) for (int i = a; i <= b; ++i)
#define rrep(i, a, b) for (int i = a; i >= b; --i)
#define FOR(i, a, b) for (int i = a; i < b; ++i)
#define pb push_back
#define MP make_pair
#define all(v) v.begin(), v.end()
#define clr(v) v.clear()
#define isEven(x) !(x & 1)
#define yes cout<<"YES"<<endl
#define no cout<<"NO"<<endl
int main() {
	ios::sync_with_stdio ( false );
	cin.tie ( 0 );
	int n, k;
	vector<int>a ( n );
	cin >> n;
	rep ( i, 0, n - 1 ) cin >> a[i];
	cin >> k;
	rep ( i, 0, n - 1 ) {
		if ( a[i] == k ) {
			cout << i;
			return 0;
		}
	}
	cout<<"-1";
	return 0;
}

```cpp
#include <bits/stdc++.h>//万能头文件
using namespace std;
long long n,a[10005],x;//用int也行
int main(){
    cin>>n;
    for (int i=0;i<n;i++){
        cin>>a[i];
    }
    cin>>x;//输入变量
    for (int i=0;i<n;i++){
        if (a[i]==x){
            cout<<i;
            return 0;
        }
    }
    cout<<-1;
    return 0;
}

# ###### 大家向我看齐！我是(sha m)!!!（哈哈哈哈哈哈哈哈哈（其实我是（傻逼）！））

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,a[10010],x;
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>a[i];
    cin>>x;
    for(int i=1;i<=n;i++)
        if(a[i]==x){
            cout<<i-1;
            return 0;
        }
    cout<<-1;
    return 0;
}

#include<bits/stdc++.h> 
using namespace std;
 int main() { 
 int n,a[123456789],k; cin>>n; 
 for (int i=0;i<n;i++){
 cin>>a[i];
 }
 cin>>k; 
 for (int i=0;i<n;i++) { 
 if (a[i]==k) {
 cout<<i;return 0;
 } 
 } 
 cout<<-1; return 0;
  }

#include<bits/stdc++.h> using namespace std; int main() { int n,a[123456789],k; cin>>n; for (int i=0;i<n;i++) cin>>a[i]; cin>>k; for (int i=0;i<n;i++) { if (a[i]==k) {cout<<i;return 0;} } cout<<-1; return 0; }