import java.io.*;
import java.math.BigDecimal;
import java.util.Arrays;
import java.util.StringJoiner;
import java.util.StringTokenizer;
import java.util.function.Function;

public class Main {

    static int N, M;
    static int[] S, T;

    public static void main(String[] args) {
        FastScanner sc = new FastScanner(System.in);
        N = sc.nextInt();
        M = sc.nextInt();
        S = new int[M];
        T = new int[M];
        for (int i = 0; i < M; i++) {
            S[i] = sc.nextInt()-1;
            T[i] = sc.nextInt()-1;
        }

        System.out.println(BigDecimal.valueOf(solve()).toPlainString());
    }

    static double solve() {
        int[][] G = adjD(N, S, T);
        double[] E = new double[N]; // goalまでの距離の期待値
        E[N-1] = 0;
        for (int a = N-2; a >= 0; a--) {
            int d = G[a].length;
            for (int b : G[a]) {
                E[a] += (E[b] + 1) / d;
            }
        }

        double[] P = new double[N]; // たどり着く確率
        P[0] = 1.0;
        for (int a = 0; a < N; a++) {
            int d = G[a].length;
            for (int b : G[a]) {
                P[b] += P[a] / d;
            }
        }

        double maxRefine = 0.0;
        for (int a = 0; a < N-1; a++) {
            int d = G[a].length;
            if( d <= 1 ) continue;

            // 一番期待値が大きい道のみ閉鎖する意味がある
            double maxE = E[G[a][0]];
            for (int i = 1; i < d; i++) {
                maxE = Math.max(maxE, E[G[a][i]]);
            }

            // 改善した期待値
            double refineE = (E[a] * d - (maxE+1)) / (d-1);

            // 改善した期待値 * 確率 が改善分
            maxRefine = Math.max(maxRefine, (E[a] - refineE) * P[a]);
        }

        return E[0] - maxRefine;
    }

    static int[][] adjD(int n, int[] from, int[] to) {
        int[][] adj = new int[n][];
        int[] cnt = new int[n];
        for (int f : from) {
            cnt[f]++;
        }
        for (int i = 0; i < n; i++) {
            adj[i] = new int[cnt[i]];
        }
        for (int i = 0; i < from.length; i++) {
            adj[from[i]][--cnt[from[i]]] = to[i];
        }
        return adj;
    }

    @SuppressWarnings("unused")
    static class FastScanner {
        private BufferedReader reader;
        private StringTokenizer tokenizer;

        FastScanner(InputStream in) {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        String next() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        String nextLine() {
            if (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    return reader.readLine();
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken("\n");
        }

        long nextLong() {
            return Long.parseLong(next());
        }

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

        int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        int[] nextIntArray(int n, int delta) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt() + delta;
            return a;
        }

        long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }
    }

    static <A> void writeLines(A[] as, Function<A, String> f) {
        PrintWriter pw = new PrintWriter(System.out);
        for (A a : as) {
            pw.println(f.apply(a));
        }
        pw.flush();
    }

    static void writeLines(int[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (int a : as) pw.println(a);
        pw.flush();
    }

    static void writeLines(long[] as) {
        PrintWriter pw = new PrintWriter(System.out);
        for (long a : as) pw.println(a);
        pw.flush();
    }

    static int max(int... as) {
        int max = Integer.MIN_VALUE;
        for (int a : as) max = Math.max(a, max);
        return max;
    }

    static int min(int... as) {
        int min = Integer.MAX_VALUE;
        for (int a : as) min = Math.min(a, min);
        return min;
    }

    static void debug(Object... args) {
        StringJoiner j = new StringJoiner(" ");
        for (Object arg : args) {
            if (arg instanceof int[]) j.add(Arrays.toString((int[]) arg));
            else if (arg instanceof long[]) j.add(Arrays.toString((long[]) arg));
            else if (arg instanceof double[]) j.add(Arrays.toString((double[]) arg));
            else if (arg instanceof Object[]) j.add(Arrays.toString((Object[]) arg));
            else j.add(arg.toString());
        }
        System.err.println(j.toString());
    }
}


Measured memory_bytes: 42840