#include <bits/stdc++.h>
using namespace std;
const long double pi = acos(-1.0);
const int intINF = (int)1e9;
template <typename T>
T gcd(T a, T b) {
  while (a > 0 && b > 0) {
    if (a > b)
      a %= b;
    else
      b %= a;
  }
  return (a + b);
}
template <typename T>
T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}
template <typename T>
bool prime(T n) {
  if (n <= 1) {
    return false;
  }
  T i = 2;
  while (i * i <= n) {
    if (n % i == 0) {
      return false;
    }
    ++i;
  }
  return true;
}
long long get_power(long long a, long long b, long long mod) {
  if (b == 0) {
    return 1 % mod;
  }
  long long ans = get_power(a, b / 2, mod);
  ans = (ans * ans) % mod;
  if (b % 2) {
    ans *= a;
  }
  ans %= mod;
  return ans;
}
template <typename T, typename U>
U power(T a, T b, U modulo) {
  long long A = (long long)a, B = (long long)b, C = (long long)modulo;
  return (U)get_power(A, B, C);
}
long long p;
long long intersect(long long l, long long r, long long val) {
  long long cnt = r - l + 1;
  cnt -= r / val - (l - 1) / val;
  return cnt;
}
long double get(long long x1, long long trololo, long long x2, long long y2) {
  long long allCount = (trololo - x1 + 1) * (y2 - x2 + 1);
  long long goodCount = intersect(x1, trololo, p) * intersect(x2, y2, p);
  return 1. * (allCount - goodCount) / allCount;
}
void solveTask() {
  int n;
  cin >> n >> p;
  long double answer = 0.;
  vector<long long> a(n), b(n);
  for (int i = 0; i < n; ++i) {
    cin >> a[i] >> b[i];
  }
  for (int i = 0; i < n; ++i) {
    answer += get(a[i], b[i], a[(i + 1) % n], b[(i + 1) % n]);
  }
  cout << fixed << setprecision(15) << answer * 2000. << endl;
}
int main() {
  ios_base::sync_with_stdio(false);
  solveTask();
  return 0;
}
