#include<cstdio>


using namespace std;


int n, m;


int a[100], b[100];





int main() {


    scanf("%d%d", &n, &m);


    for (int i = 1; i <= n; ++i)


        a[i] = b[i] = 0;


    for (int i = 1; i <= m; ++i) {


        int x, y;


        scanf("%d%d", &x, &y);


        if (a[x] < y && b[y] < x) {


            if (a[x] > 0)


                b[a[x]] = 0;


            if (b[y] > 0)


                a[b[y]] = 0;


            a[x] = y;


            b[y] = x;


        }


    }


    int ans = 0;


    for (int i = 1; i <= n; ++i) {


        if (a[i] == 0)


            ++ans;


        if (b[i] == 0)


            ++ans;


    }


    printf("%d", ans);


    return 0;


}

假设输入的n和m都是正整数，x和y都是在［1, n］的范围内的整数，完成下面的判断题和单选题：

判断题

选择题