thing1

/**
 * meyer88
 * $SRCFILE
 */

#include <assert.h>
#include <ctype.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <algorithm>
#include <bitset>
#include <deque>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

typedef long long int lli;
typedef pair<int, int> pii;
typedef pair<lli, lli> pll;

int gInt () {
  int i;
  scanf("%d", &i);
  return i;
}

pii g2Int () {
  pii xy;
  scanf("%d %d", &xy.first, &xy.second);
  return xy;
}

pll g2Long () {
  pll xy;
  scanf("%lld %lld", &xy.first, &xy.second);
  return xy;
}

lli gLong () {
  lli i;
  scanf("%lld", &i);
  return i;
}

double gDouble () {
  double i;
  scanf("%lf", &i);
  return i;
}

void quit () {
  fflush(stdout);
  exit(0);
}

int main (int argc, char ** argv) {
  int n = gInt();
  int k = gInt();
  bool ary[n][2];
  int rank[2*n];
  int ai[2*n];
  int aj[2*n];
  std::map<int, pii> m;
  int h=0;
  int ret = 0;

  for(int i = 0; i < n; i++) {
    ary[i][0] = false;
    ary[i][1] = false;
    ret += rank[h] = gInt();
    ai[h] = i;
    aj[h] = 0;
    h++;
    ret += rank[h] = gInt();
    ai[h] = i;
    aj[h] = 1;
    h++;
  }

  int i, j, tmp;
  for (i = 1; i < h; i++) {
    j = i;
    while (j > 0 && rank[j - 1] > rank[j]) {
      tmp = rank[j];
      rank[j] = rank[j - 1];
      rank[j - 1] = tmp;
      tmp = ai[j];
      ai[j] = ai[j - 1];
      ai[j - 1] = tmp;
      tmp = aj[j];
      aj[j] = aj[j - 1];
      aj[j - 1] = tmp;
      j--;
    }
  }

  int kk=0;
  for(int fd = 0; fd < h; fd++) {
    i = ai[fd]; j = aj[fd];
    int kuju = (j == 1) ? 0 : 1;
    if(i == 0 && ary[i][kuju] || ary[i+1][kuju]) {
      continue;
    }
    else if(i == n-1 && ary[i-1][kuju] || ary[i][kuju]) {
      continue;
    }
    else if(ary[i-1][kuju] || ary[i][kuju] || ary[i+1][kuju]) {
      continue;
    }
    ary[i][j] = true;
    ret -= rank[fd];
    kk++;
    if(kk == k) {
      break;
    }
  }

  printf("%d\n", ret);

  quit();
}