#include <bits/stdc++.h>
using namespace std;
struct node {
  int l, r, id;
  node() {}
  node(int l1, int r1, int id1) : l(l1), r(r1), id(id1) {}
  inline bool operator<(const node &y) const { return l < y.l; }
};
set<node> st;
vector<pair<int, int> > v[300010];
int c[300010], n, k;
inline int rd() {
  int x = 0;
  char ch = getchar();
  for (; ch < '0' || ch > '9'; ch = getchar())
    ;
  for (; ch >= '0' && ch <= '9'; ch = getchar()) x = x * 10 + ch - '0';
  return x;
}
inline set<node>::iterator split(int x) {
  set<node>::iterator it = st.upper_bound(node(x, 0, 0));
  it--;
  node hh = *it;
  if (hh.l == x) return it;
  st.erase(hh);
  st.insert(node(hh.l, x - 1, hh.id));
  st.insert(node(x, hh.r, hh.id));
  return st.lower_bound(node(x, hh.r, hh.id));
}
inline long long querycnt(int mid) {
  memset(c, 0, sizeof(c));
  long long ans = 0, res = 0;
  int now = 1;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j < v[i].size(); j++) {
      pair<int, int> hh = v[i][j];
      c[hh.first] += hh.second;
      if (hh.first <= now) res += hh.second;
    }
    while (res >= mid) {
      for (int j = 0; j < v[now].size(); j++) res -= v[now][j].second;
      now++;
      res += c[now];
    }
    ans += now - 1;
  }
  return ans;
}
inline long long querysum(int mid) {
  memset(c, 0, sizeof(c));
  long long ans = 0, res1 = 0, res2 = 0;
  int now = 1;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j < v[i].size(); j++) {
      pair<int, int> hh = v[i][j];
      c[hh.first] += hh.second;
      if (hh.first <= now)
        res1 += hh.second, res2 += (long long)hh.first * hh.second;
    }
    while (res1 >= mid) {
      for (int j = 0; j < v[now].size(); j++) {
        pair<int, int> hh = v[now][j];
        res1 -= hh.second;
        res2 -= (long long)hh.first * hh.second;
        ans += (long long)hh.second * (now - hh.first + 1) * (n - i + 1);
      }
      now++;
      res1 += c[now];
      res2 += (long long)c[now] * now;
    }
    ans += res1 * now - res2;
  }
  return ans;
}
int main() {
  n = rd();
  k = rd();
  st.insert(node(1, 1000000000, 0));
  for (int i = 1; i <= n; i++) {
    int x = rd(), y = rd() - 1;
    set<node>::iterator l = split(x), r = split(y + 1);
    for (set<node>::iterator it = l; it != r; it++)
      v[i].push_back(pair<int, int>((*it).id + 1, (*it).r - (*it).l + 1));
    st.erase(l, r);
    st.insert(node(x, y, i));
  }
  int l = 1, r = 1000000000;
  while (l < r) {
    int mid = ((l + r) >> 1) + 1;
    if (querycnt(mid) >= k)
      l = mid;
    else
      r = mid - 1;
  }
  printf("%lld\n", querysum(l) - (long long)(querycnt(l) - k) * l);
  return 0;
}
