#include<bits/stdc++.h>
using namespace std;
struct Seg{
	int l,r;
	bool operator <(const Seg s) const {
		return l!=s.l?l<s.l:r>s.r;
	}
}a[100005],b[100005];
int n,N,m,f[100005][105],ans=0;
int main(){
	cin>>N>>m;
	for(int i=1;i<=N;i++)cin>>b[i].l>>b[i].r;
	sort(b+1,b+N+1);
	for(int i=1,cur=-1;i<=N;i++)if(cur<b[i].r)cur=b[i].r,a[++n]=b[i];else m=max(m-1,0);
	memset(f,0xc0,sizeof(f)),f[0][0]=0;
	for(int i=1;i<=n;i++){
		for(int j=0;j<=m;j++){
			for(int k=i-1;k>=0&&k>=i-j-1;k--)f[i][j]=max(f[i][j],f[k][j-(i-k-1)]+a[i].r-max(a[i].l,a[k].r));
		}
		ans=max(ans,f[i][max(0,m-(n-i))]);
	}
	cout<<ans;
}