//#define NDEBUG
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iostream>
#include <vector>

namespace n91 {

using i8 = std::int_fast8_t;
using i32 = std::int_fast32_t;
using i64 = std::int_fast64_t;
using u8 = std::uint_fast8_t;
using u32 = std::uint_fast32_t;
using u64 = std::uint_fast64_t;
using isize = std::ptrdiff_t;
using usize = std::size_t;

struct rep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { ++i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr rep(const usize f, const usize l) noexcept
      : f(std::min(f, l)), l(l) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
struct revrep {
  struct itr {
    usize i;
    constexpr itr(const usize i) noexcept : i(i) {}
    void operator++() noexcept { --i; }
    constexpr usize operator*() const noexcept { return i; }
    constexpr bool operator!=(const itr x) const noexcept { return i != x.i; }
  };
  const itr f, l;
  constexpr revrep(const usize f, const usize l) noexcept
      : f(l - 1), l(std::min(f, l) - 1) {}
  constexpr auto begin() const noexcept { return f; }
  constexpr auto end() const noexcept { return l; }
};
template <class T> auto md_vec(const usize n, const T &value) {
  return std::vector<T>(n, value);
}
template <class... Args> auto md_vec(const usize n, Args... args) {
  return std::vector<decltype(md_vec(args...))>(n, md_vec(args...));
}
template <class T> constexpr T difference(const T &a, const T &b) noexcept {
  return a < b ? b - a : a - b;
}
template <class T> void chmin(T &a, const T &b) noexcept {
  if (b < a)
    a = b;
}
template <class T> void chmax(T &a, const T &b) noexcept {
  if (a < b)
    a = b;
}
template <class T> T scan() {
  T ret;
  std::cin >> ret;
  return ret;
}

} // namespace n91
#include <algorithm>
#include <utility>
#include <vector>

namespace n91 {

template <class T> std::vector<T> divisors(const T &n) {
  std::vector<T> ret;
  T i = static_cast<T>(1);
  while (i * i < n) {
    if (n % i == static_cast<T>(0)) {
      ret.push_back(i);
      ret.push_back(n / i);
    }
    ++i;
  }
  if (i * i == n) {
    ret.push_back(i);
  }
  std::sort(ret.begin(), ret.end());
  ret.shrink_to_fit();
  return std::move(ret);
}

} // namespace n91

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <iostream>
#include <limits>
#include <numeric>
#include <utility>

namespace n91 {

void main_() {
  /*
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  //*/
  const usize n = scan<usize>();
  const usize m = scan<usize>();
  auto g = md_vec(n, 0, usize()), rg = g;
  for (const usize i : rep(0, m)) {
    const usize s = scan<usize>() - 1;
    const usize t = scan<usize>() - 1;
    g[s].push_back(t);
    rg[t].push_back(s);
  }
  std::vector<double> ex(n, 0);
  ex[n - 1] = 0;
  for (const usize i : revrep(0, n - 1)) {
    for (const auto e : g[i]) {
      ex[i] += ex[e];
    }
    ex[i] = ex[i] / g[i].size() + 1;
  }
  const auto calc = [&](const usize s, const usize t) {
    std::vector<double> ex2(n, 0);
    ex2[n - 1] = 0;
    for (const usize i : revrep(0, n - 1)) {
      usize deg = 0;
      for (const auto e : g[i]) {
        if (i != s || e != t) {
          ++deg;
          ex2[i] += ex2[e];
        }
      }
      ex2[i] = ex2[i] / deg + 1;
    }
    return ex2[0];
  };
  double ans = ex[0];
  for (const usize i : rep(0, n - 1)) {
    if (g[i].size() != 1) {
      usize maxt = g[i][0];
      for (const auto e : g[i]) {
        if (ex[maxt] < ex[e]) {
          maxt = e;
        }
      }
      chmin(ans, calc(i, maxt));
    }
  }
  std::cout << std::setprecision(10) << ans << std::endl;
}

} // namespace n91

int main() {
  n91::main_();
  return 0;
}


Measured memory_bytes: 4864