#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-ffloat-store")
#pragma GCC optimize("-fno-defer-pop")
long long int power(long long int a, long long int b, long long int m) {
  if (b == 0) return 1;
  if (b == 1) return a % m;
  long long int t = power(a, b / 2, m) % m;
  t = (t * t) % m;
  if (b & 1) t = ((t % m) * (a % m)) % m;
  return t;
}
long long int modInverse(long long int a, long long int m) {
  return power(a, m - 2, m);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int i, j, k, l, n, p;
  cin >> n >> p;
  long long int ar[n + 1][2];
  long double tk[n + 2];
  for (i = 1; i <= n; i++) {
    cin >> ar[i][0] >> ar[i][1];
  }
  for (i = 1; i <= n; i++) {
    tk[i] = (1.0L) * (ar[i][1] / p - (ar[i][0] - 1) / p) /
            (ar[i][1] - ar[i][0] + 1);
  }
  long double an = 0.0;
  tk[n + 1] = tk[1];
  for (i = 1; i <= n; i++) {
    an += (tk[i] + tk[i + 1] - tk[i] * tk[i + 1]);
  }
  an = an * 2000;
  cout << fixed << setprecision(10) << an;
  return 0;
}
