Remove Multiples

#include <bits/stdc++.h>
using namespace std;

int main() {
    int t;
    cin>>t;

    while(t--)
    {
        int n, m;
        cin>>n>>m;

        vector<int> a(m);
        for(auto &e: a)
            cin>>e;

        long long int suma = accumulate(a.begin(), a.end(), 0ll);
        long long int tot = ((n*1ll*(n+1))/2);

        cout<<tot - suma<<"\n";
    }
}