#include<stdio.h>
int main() {
    int m, n;
    int count = 0;
    scanf("%d", &m);
    scanf("%d", &n);
    int tree[10001] = {0};
    int a, b;
    for (int i = 1; i <= n; i++) {
        scanf("%d", &a);
        scanf("%d", &b);
        for (int j = a; j <= b; j++) {
            if(tree[j]==0)
            tree[j]++;
        }
    }
    for (int i = 0; i < m; i++) {
        if(tree[i]==1)
            count++;
    }
    printf("%d",count);
}

各位大佬帮忙看看