【題目敘述】https://zerojudge.tw/ShowProblem?problemid=e968
#include <bits/stdc++.h>
using namespace std;
int n, a[25];
int main(){
cin >> n;
for (int i = 0; i < 3; i++){
int m;
cin >> m;
a[m] = 1;
}
for (int i = n; i > 0; i--){
if (!a[i]) cout << "No. " << i << "\n";
}
}