bat cau

#include <bits/stdc++.h>

using namespace std;
int l[1000][1000] , a[1000][1000] , n , m;
vector <pair<int , int>> kq;
void qhd()
{
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
        if (a[i][j] == 1) l[i][j] = l[i - 1][j - 1] + 1;
        else l[i][j] = max(l[i - 1][j] , l[i][j - 1]);
    cout << l[n][m] << endl;
    int i = n , j = m;
    while ((i > 0) && (j > 0))
    if (a[i][j] == 1)
    {
        kq.push_back({i , j});
        i--; j--;
    } else if (l[i - 1][j] > l[i][j - 1]) i--;
           else j--;
}
int main()
{
    freopen ("f.inp" , "r" , stdin);
    freopen ("f.out" , "w" , stdout);
    cin >> n >> m;
    int u , v;
    while (cin >> u >> v)
    {
        a[u][v] = 1;
        a[v][u] = 1;
    }
    qhd();
    reverse (kq.begin() , kq.end());
    for (auto x : kq)
    cout << x.first << " " << x.second << endl;
    return 0;
}