import java.io.InputStreamReader;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author Rubanenko
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		Dag solver = new Dag();
		solver.solve(1, in, out);
		out.close();
	}
}

class Dag {

    public void solve(int testNumber, InputReader in, PrintWriter out) {
        int n = in.nextInt();
        boolean[][] a = new boolean[n + 1][n + 1];
        boolean[][] newEdge = new boolean[n + 1][n + 1];
        boolean[] used = new boolean[n + 1];
        int[] outDegree = new int[n + 1];
        int numberOfEdges = (n * (n - 1)) / 2;
        for (int i = 0; i < n; i++) {
           String s = in.next();
           for (int j = 0; j < n; j++) {
               a[i][j] = (s.charAt(j) == '1');
               if (a[i][j]) {
                   numberOfEdges--;
                   outDegree[i]++;
               }
           }
        }
        out.println(numberOfEdges);
        for (int i = 0; i < n; i++) {
            int v = -1;
            for (int j = n - 1; j >= 0; j--) {
                if (!used[j] && outDegree[j] == 0) {
                    v = j;
                    break;
                }
            }
            used[v] = true;
            for (int j = 0; j < n; j++) {
                if (j != v && !a[j][v] && !used[j]) {
                    newEdge[j][v] = true;
                }
            }
            for (int j = 0; j < n; j++) {
                if (a[j][v]) outDegree[j]--;
            }
        }
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                if (newEdge[i][j]) out.println((i + 1) + " " + (j + 1));
            }
        }
    }
}

class InputReader {
    private BufferedReader reader;
    private StringTokenizer tokenizer;

    public InputReader(InputStream inputStream) {
        reader = new BufferedReader(new InputStreamReader(inputStream));
    }

    public String nextLine() {
        String line = null;
        try {
            line = reader.readLine();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return line;
    }

    public String next() {
        while (tokenizer == null || !tokenizer.hasMoreTokens())
            tokenizer = new StringTokenizer(nextLine());
        return tokenizer.nextToken();
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }
}