#include <bits/stdc++.h>
using namespace std;
long long spf[3000001];
long long fac[3000001];
void sieve() {
  spf[1] = 1;
  for (long long i = 2; i < 3000001; i++) spf[i] = i;
  for (long long i = 4; i < 3000001; i += 2) spf[i] = 2;
  for (long long i = 3; i * i < 3000001; i++) {
    if (spf[i] == i) {
      for (long long j = i * i; j < 3000001; j += i)
        if (spf[j] == j) spf[j] = i;
    }
  }
}
map<long long, long long> getfactor(long long a) {
  map<long long, long long> m;
  while (a > 1) {
    m[spf[a]]++;
    a /= spf[a];
  }
  return m;
}
long long power(long long x, long long y, long long p) {
  long long res = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1) res = (res * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return res;
}
long long gcd(long long a, long long b) {
  if (a == 0) return b;
  return gcd(b % a, a);
}
long long inverse(long long a, long long p) { return power(a, p - 2, p); }
long long ncr(long long n, long long r, long long p) {
  if (r > n) return 0;
  if (r == 0) return 1;
  return (fac[n] * inverse(fac[r], p) % p * inverse(fac[n - r], p) % p) % p;
}
void solve() {
  long long n, k;
  cin >> n >> k;
  map<long long, long long> m;
  for (long long i = 1; i <= n; i++) {
    long long l, r;
    cin >> l >> r;
    m[l]++;
    m[r + 1]--;
  }
  long long pre = 0;
  for (auto it : m) {
    pre += m[it.first];
    m[it.first] = pre;
  }
  long long prev = -1e18, val = 0;
  long long ans = 0;
  for (auto it : m) {
    if (prev == -1e18) {
      prev = it.first;
      val = it.second;
    } else {
      ans = (ans +
             (ncr(val, k, 1000000007) * (it.first - prev) % 1000000007) %
                 1000000007 +
             1000000007) %
            1000000007;
      prev = it.first;
      val = it.second;
    }
  }
  cout << ans << '\n';
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long test = 1;
  fac[0] = 1;
  for (long long i = 1; i <= 300000; i++)
    fac[i] = (fac[i - 1] * i) % 1000000007;
  while (test--) {
    solve();
  }
}
