MATCH1

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

const int N = 105;

int n, k;
vector<int> g[N];
int used[N];
int match[N];
int timer, ans;

bool try_kuhn(int u) {
    if(used[u] == timer) return false;

    used[u] = timer;
    for(int v : g[u]) {
        if(match[v] == 0 || try_kuhn(match[v])) {
            match[v] = u;
            return true;
        }
    }
    return false;
}

int main() {
    //freopen("in.txt", "r", stdin);
    //freopen("MATCH1.inp", "r", stdin);
    //freopen("MATCH1.out", "w", stdout);
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);

    cin >> n >> k;

    int u, v;
    while(cin >> u >> v) {
        g[u].push_back(v);
    }

    timer = ans = 0;
    for(int i = 1; i <= n; ++i) {
        timer++;
        ans += try_kuhn(i);
    }

    cout << ans << '\n';

    for(int i = 1; i <= k; ++i) {
        if(match[i])
            cout << match[i] << ' ' << i << '\n';
    }

    return 0;
}