#include<cstdio>

#include<algorithm>

#define N 210

using namespace std;

int n,m,i,j,flag,cb,cc,s[N],f[N][N],ans=-2147400000;

struct P{int x,y;}a[N],b[N],c[N];

bool cmpb(P a,P b){return a.y-a.x>b.y-b.x;}

bool cmpc(P a,P b){return a.x<b.x;}

void dp(int p,int l,int r,int dl,int dr){

  int m=(l+r)>>1,dm=dl,t=ans;

  for(int i=min(m-1,dr);i>=dl;i--){

    if(c[i+1].y<=c[m].x)break;

    int now=f[p-1][i]+c[i+1].y-c[m].x;

    if(now>=t)t=now,dm=i;

  }

  f[p][m]=t;

  if(l<m)dp(p,l,m-1,dl,dm);

  if(r>m)dp(p,m+1,r,dm,dr);

}

int main(){

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

  for(i=1;i<=n;i++)scanf("%d%d",&a[i].x,&a[i].y);

  for(i=1;i<=n;i++){

    for(flag=0,j=1;j<=n;j++)if(a[i].x<=a[j].x&&a[j].y<=a[i].y&&(a[i].x!=a[j].x||a[i].y!=a[j].y||i<j)){flag=1;break;}

    if(flag)b[++cb]=a[i];else c[++cc]=a[i];

  }

  sort(b+1,b+cb+1,cmpb);

  for(i=1;i<=cb;i++)s[i]=s[i-1]+b[i].y-b[i].x;

  sort(c+1,c+cc+1,cmpc);

  for(i=1;i<=cc;i++)f[0][i]=ans;

  for(i=1;i<=m;i++)f[i][0]=ans;

  for(i=1;i<=m;i++)dp(i,1,cc,0,cc);

  for(i=1;i<=m;i++)if(m-i<=cb&&f[i][cc]>=0)ans=max(ans,f[i][cc]+s[m-i]);

  return printf("%d",ans),0;

}