#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5 + 5;
double prob[maxn];
int main() {
  ios::sync_with_stdio(false);
  int n, p;
  while (cin >> n >> p) {
    int l, r;
    for (int i = 0; i < n; ++i) {
      cin >> l >> r;
      prob[i] = (double)(r / p - (l - 1) / p) / (r + 1 - l);
    }
    double sum = 0;
    for (int i = 0; i < n; ++i) {
      int j = (i + 1) % n;
      sum += 1.0 - (1 - prob[i]) * (1 - prob[j]);
    }
    printf("%.8lf\n", sum * 2000);
  }
  return 0;
}
