#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
long long fac[200001];
long long inv[200001];
long long modexp(long long b, long long e) {
  long long ans = 1;
  while (e > 0) {
    if (e & 1) {
      ans = (ans * b) % mod;
    }
    b = (b * b) % mod;
    e >>= 1;
  }
  return ans;
}
long long comb(long long n, long long k) {
  long long ans = (fac[n] * inv[k]) % mod;
  ans = (ans * inv[n - k]) % mod;
  return ans;
}
int main() {
  fac[0] = fac[1] = 1;
  inv[0] = inv[1] = 1;
  for (int i = 2; i <= 200000; i++) {
    fac[i] = (fac[i - 1] * i) % mod;
    inv[i] = modexp(fac[i], mod - 2);
  }
  int n, k;
  cin >> n >> k;
  vector<pair<int, int> > list;
  for (int i = 1; i <= n; i++) {
    int a, b;
    cin >> a >> b;
    list.push_back(make_pair(a, 1));
    list.push_back(make_pair(b + 1, -1));
  }
  sort(list.begin(), list.end());
  int maintain = 0;
  long long ans = 0;
  int selisih;
  for (int i = 0; i < list.size(); i++) {
    if (i > 0 && list[i].first != list[i - 1].first) {
      if (maintain >= k) {
        ans += comb(maintain, k) * (list[i].first - selisih);
        ans %= mod;
      }
    }
    maintain += list[i].second;
    selisih = list[i].first;
  }
  cout << ans << endl;
}
