/*
	Name:
	Date: 04/11/14 08:24
	Description:
	Analysis:
*/
#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
int ans=0,n,m,k;
bool a[705][705],b[705][705];
int dx[15]={0,-1,0 ,0,1};
int dy[15]={0, 0,-1,1,0};
void DFS(int x,int y,int sum)
{
	if(sum>ans) ans=sum;
	for(int i=1;i<=4;i++){
		if(x+dx[i]<=n && x+dx[i]>=1 && y+dy[i]>=1 && y+dy[i]<=m)
		if(a[x+dx[i]][y+dy[i]] && !b[x+dx[i]][y+dy[i]]){
			b[x+dx[i]][y+dy[i]]=1;
			DFS(x+dx[i],y+dy[i],sum+1);
			b[x+dx[i]][y+dy[i]]=0;
		}
	}
	return ;
}
int main()
{
	freopen("lake.in","r",stdin);
	freopen("lake.out","w",stdout);
	scanf("%d%d%d",&n,&m,&k);
	
	for(int i=1,x,y;i<=k;i++){
		scanf("%d%d",&x,&y);
		a[x][y]=1;
	}

	for(int i=1;i<=n;i++){
		for(int j=1;j<=m;j++){
			if(a[i][j] && !b[i][j] ){
				b[i][j]=1;
				DFS(i,j,1);
				b[i][j]=0;
			}
		}
	}
	printf("%d",ans);
	fclose(stdin);
	fclose(stdout);
	//while(1);
	return 0;
}