#include<bits/stdc++.h>
using namespace std;
int n,k;
int arr[15][15];
int maxx=1;
struct node{
	int x,y,sum;
};
queue<node> q;
int main(){
	freopen("csp2022pj_point.in", "r", stdin);
	freopen("csp2022pj_point.out", "w", stdout); 
	cin>>n>>k;
	int x,y;
	for(int i=1;i<=n;i++){
		cin>>x>>y;
		arr[x][y]=1;
	}
	for(int i=0;i<=10;i++){
		for(int j=0;j<=10;j++){
			if(arr[x][y]==1){
				q.push(node{x,y,1});
				while(!q.empty()){
					node h=q.front();q.pop();
					if(arr[h.x+1][h.y]==1){
						q.push(node{h.x+1,h.y,h.sum+1});
						maxx=max(maxx,h.sum+1);
					}
					if(arr[h.x][h.y+1]==1){
						q.push(node{h.x,h.y+1,h.sum+1});
						maxx=max(maxx,h.sum+1);
					}
				}
			}
		}
	}
	cout<<maxx;
	return 0;
}