#include <bits/stdc++.h>
using namespace std;
long long fat[200005];
void gerafat() {
  fat[0] = 1;
  for (long long i = 1; i < 200005; i++) {
    fat[i] = (fat[i - 1] * i) % 1000000007;
  }
}
long long modInv(long long a) {
  long long v = 1;
  long long e = 1000000007 - 2;
  while (e) {
    if (e % 2) {
      v *= a;
      v %= 1000000007;
    }
    e /= 2;
    a *= a;
    a %= 1000000007;
  }
  return v;
}
long long comb(int a, int b) {
  if (a < b) return 0;
  long long res =
      ((fat[a] * modInv(fat[b])) % 1000000007 * modInv(fat[a - b])) %
      1000000007;
  return res;
}
int main() {
  long long n, k;
  cin >> n >> k;
  gerafat();
  vector<long long> num(0);
  set<long long> sete;
  vector<pair<long long, long long> > v(n, {0, 0});
  for (long long i = 0; i < n; i++) {
    long long a, b;
    cin >> a >> b;
    v[i] = {a, b};
    if (!sete.count(a)) {
      num.push_back(a);
      sete.insert(a);
    }
    if (!sete.count(b)) {
      num.push_back(b);
      sete.insert(b);
    }
    if (!sete.count(b + 1)) {
      num.push_back(b + 1);
      sete.insert(b + 1);
    }
  }
  sort(num.begin(), num.end());
  long long tam = num.size();
  map<long long, long long> mapa;
  for (long long i = 0; i < tam; i++) mapa[num[i]] = i;
  vector<long long> pref(tam, 0);
  for (int i = 0; i < n; i++) {
    pref[mapa[v[i].first]]++;
    pref[mapa[v[i].second + 1]]--;
  }
  for (int i = 1; i < tam; i++) pref[i] += pref[i - 1];
  long long res = comb(pref[0], k) % 1000000007;
  for (long long i = 1; i < tam; i++) {
    res = (res + comb(pref[i], k)) % 1000000007;
    res = (res + ((long long)(num[i] - num[i - 1] - 1) *
                  comb(min(pref[i], pref[i - 1]), k)) %
                     1000000007) %
          1000000007;
  }
  cout << res << endl;
}
