#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n, m;
    cin >> n >> m;
    vector <vector<int>> mass(n, vector <int>());
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--; b--;
        mass[a].push_back(b);
    }
    cout << n << endl;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cout << mass[i][j] << " ";
        }
    }
    return 0;
}