题解 | #序列找数#

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);
        int i = 0;
        int max = in.nextInt();
        int sum = 0;
        int tmp = 0;
        for (; in.hasNextInt(); i++) {
            tmp += in.nextInt();
        }
        if (max != i){
            System.out.println(i);
            return;
        }
        sum = ((1 + i) * i) / 2;
        System.out.println(sum - tmp);
    }
}