#include <iostream>

#include <sstream>

#include <algorithm>

#include <cstdio>

#include <math.h>

#include <set>

#include <map>

#include <queue>

#include <string>

#include <string.h>

#include <bitset>

#include <unordered_map>

#define REP(i,a,n) for(int i=a;i<=n;++i)

#define PER(i,a,n) for(int i=n;i>=a;--i)

#define hr putchar(10)

#define pb push_back

#define lc (o<<1)

#define rc (lc|1)

#define mid ((l+r)>>1)

#define ls lc,l,mid

#define rs rc,mid+1,r

#define x first

#define y second

#define io std::ios::sync_with_stdio(false)

#define endl '\n'

#define DB(a) ({REP(__i,1,n) cout<<a[__i]<<' ';hr;})

using namespace std;

typedef long long ll;

typedef pair<int,int> pii;

const int P = 1e9+7, P2 = 998244353, INF = 0x3f3f3f3f;

ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}

ll qpow(ll a,ll n) {ll r=1%P;for (a%=P;n;a=a*a%P,n>>=1)if(n&1)r=r*a%P;return r;}

ll inv(ll x){return x<=1?1:inv(P%x)*(P-P/x)%P;}

inline int rd() {int x=0;char p=getchar();while(p<'0'||p>'9')p=getchar();while(p>='0'&&p<='9')x=x*10+p-'0',p=getchar();return x;}

//head

#ifdef ONLINE_JUDGE

const int N = 1e6+10;

#else

const int N = 999;

#endif

int n, m, k, S, T;

struct _ {int from,to,w,f;};

vector<_> E;

vector<int> g[N];

int a[N], pre[N], inq[N], d[N];

int mf,mc;

queue<int> q;

void add(int x, int y, int c, int w) {

    g[x].pb(E.size());

    E.pb({x,y,c,w});

    g[y].pb(E.size());

    E.pb({y,x,0,-w});

}

void mfmc() {

	mf=mc=0;

    while (1) {

        REP(i,1,T) a[i]=d[i]=INF,inq[i]=0;

        q.push(S),d[S]=0;

        while (!q.empty()) {

            int x=q.front(); q.pop();

            inq[x] = 0;

            for (auto t:g[x]) {

                auto e=E[t];

                if (e.w>0&&d[e.to]>d[x]+e.f) {

                    d[e.to]=d[x]+e.f;

                    pre[e.to]=t;

                    a[e.to]=min(a[x],e.w);

                    if (!inq[e.to]) {

                        inq[e.to]=1;

                        q.push(e.to);

                    }

                }

            }

        }

        if (a[T]==INF) break;

        for (int u=T;u!=S;u=E[pre[u]].from) {

            E[pre[u]].w-=a[T];

            E[pre[u]^1].w+=a[T];

        }

        mf+=a[T],mc+=a[T]*d[T];

    }

}

int b[N], l[N], r[N];

int main() {

	scanf("%d%d", &n, &k);

	REP(i,1,n) {

		scanf("%d%d",l+i,r+i);

		b[++*b]=l[i],b[++*b]=r[i];

	}

	sort(b+1,b+1+*b),*b=unique(b+1,b+1+*b)-b-1;

	REP(i,1,n) {

		l[i]=lower_bound(b+1,b+1+*b,l[i])-b;

		r[i]=lower_bound(b+1,b+1+*b,r[i])-b;

	}

	S = *b+1, T = S+1;

	add(S,1,k,0),add(*b,T,k,0);

	REP(i,2,*b) add(i-1,i,k,0);

	REP(i,1,n) add(l[i],r[i],1,-b[r[i]]+b[l[i]]);

	mfmc();

	printf("%d\n", -mc);

}