/*                                                                                
                      Keyblinds Guide
     				###################
      @Ntsc 2024

      - Ctrl+Alt+G then P : Enter luogu problem details
      - Ctrl+Alt+B : Run all cases in CPH
      - ctrl+D : choose this and dump to the next
      - ctrl+Shift+L : choose all like this
      - ctrl+K then ctrl+W: close all
      - Alt+la/ra : move mouse to pre/nxt pos'
	  
*/
#include <bits/stdc++.h>
#include <queue>
using namespace std;

#define rep(i, l, r) for (int i = l, END##i = r; i <= END##i; ++i)
#define per(i, r, l) for (int i = r, END##i = l; i >= END##i; --i)
#define pb push_back
#define mp make_pair
#define int long long
#define ull unsigned long long
#define pii pair<int, int>
#define ps second
#define pf first

// #define innt int
#define itn int
// #define inr intw
// #define mian main
// #define iont int

#define rd read()
int read(){
    int xx = 0, ff = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
		if (ch == '-')
			ff = -1;
		ch = getchar();
    }
    while (ch >= '0' && ch <= '9')
      xx = xx * 10 + (ch - '0'), ch = getchar();
    return xx * ff;
}
void write(int out) {
	if (out < 0)
		putchar('-'), out = -out;
	if (out > 9)
		write(out / 10);
	putchar(out % 10 + '0');
}


#define zerol = 1
#ifdef zerol
#define cdbg(x...) do { cerr << #x << " -> "; err(x); } while (0)
void err() { cerr << endl; }
template<template<typename...> class T, typename t, typename... A>
void err(T<t> a, A... x) { for (auto v: a) cerr << v << ' '; err(x...); }
template<typename T, typename... A>
void err(T a, A... x) { cerr << a << ' '; err(x...); }
#else
#define dbg(...)
#endif


const int N = 3e5 + 5;
const int INF = 1e18;
const int M = 1e7;
const int MOD = 1e9 + 7;

struct Node{
    int l,r;
}t[N];


bool cmp(Node a,Node b){
    if(a.r==b.r)return a.l<b.l;
    return a.r<b.r;
}

inline int popcnt(int x){
    int res=0;
    while(x){
        res+=x&1;
        x>>=1;

    }
    return res;
}
int n;
int K;
int ans;

void check(int s){
    
    int res=0;
    int pre=0;
    for(int i=0;i<n;i++){
        if(s>>i&1)continue;
        res+=t[i].r-max(t[i].l-1,pre);
        pre=t[i].r;        
    }

    ans=max(res,ans);
}

void solve(){
    n=rd,K=rd;
    for(int i=0;i<n;i++){
        t[i].l=rd+1;
        t[i].r=rd;
    }


    sort(t,t+n,cmp);
    for(int i=0;i<(1<<n);i++){
        if(popcnt(i)!=K)continue;
        check(i);
    }

    cout<<ans<<endl;
}

signed main() {
    // freopen(".in","r",stdin);
    // freopen(".in","w",stdout);

    int T=1;
    while(T--){
    	solve();
    }
    return 0;
}