UVA 10667

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

const int OO = 1e9;
const double EPS = 1e-9;

int arr[105][105];
int pre[105][105];

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    int t;
    cin >> t;
    while(t--) {
        int s,b;
        cin >> s >> b;
        for(int i = 1; i <= s; i++) {
            for(int j = 1; j <= s; j++) {
                arr[i][j] = 0;
            }
        }
        for(int bi = 0; bi < b; bi++) {
            int r1,c1,r2,c2;
            cin >> r1 >> c1 >> r2 >> c2;
            for(int r = r1; r <= r2; r++) {
                for(int c = c1; c <= c2; c++) {
                    arr[r][c] = 1;
                }
            }
        }
        for(int r = 1; r <= s; r++) {
            int sum = 0;
            for(int c = 1; c <= s; c++) {
                sum += arr[r][c];
                pre[r][c] = sum + pre[r-1][c];
            }
        }
        int ans = 0;
        for(int r1 = 1; r1 <= s; r1++) {
            for(int r2 = r1; r2 <= s; r2++) {
                int sum = 0;
                for(int c = 1; c <= s; c++) {
                    int curr = pre[r2][c] - pre[r2][c-1] - pre[r1-1][c] + pre[r1-1][c-1];
                    if(curr == 0) {
                        sum += r2-r1+1;
                    }
                    else {
                        sum = 0;
                    }
                    ans = max(ans,sum);
                }
            }
        }
        cout << ans << "\n";
    }
    return 0;
}