#include <bits/stdc++.h>
using namespace std;
struct Ev {
  int pos;
  bool st;
  Ev(int pos, bool st) : pos(pos), st(st) {}
  inline bool operator<(const Ev &rhs) const { return pos < rhs.pos; }
};
int n, k;
vector<Ev> ev;
int f[200005], rf[200005];
const int MOD = 1e9 + 7;
int c(int n, int k) { return (long long)f[n] * rf[k] % MOD * rf[n - k] % MOD; }
int binPow(long long x, int p) {
  long long res = 1;
  while (p) {
    if (p & 1) res = res * x % MOD;
    p >>= 1;
    if (p) x = x * x % MOD;
  }
  return (int)res;
}
int main() {
  f[0] = rf[0] = 1;
  for (int i = 1; i < 200005; ++i) {
    f[i] = (long long)f[i - 1] * i % MOD;
    rf[i] = binPow(f[i], MOD - 2);
  }
  scanf("%d%d", &n, &k);
  for (int i = 0; i < (int)(n); ++i) {
    int from, to;
    scanf("%d%d", &from, &to);
    ev.push_back(Ev(from, true));
    ev.push_back(Ev(to + 1, false));
  }
  int pre = -1e9 - 1234;
  sort(ev.begin(), ev.end());
  int cnt = 0;
  int ans = 0;
  for (Ev e : ev) {
    if (cnt >= k) {
      ans = (ans + (long long)c(cnt, k) * (e.pos - pre)) % MOD;
    }
    pre = e.pos;
    if (e.st)
      ++cnt;
    else
      --cnt;
  }
  printf("%d\n", ans);
  return 0;
}
