ll h,w,a[500][500];
ll f(ll y,ll x:Memoize){
	ll b=a[y][x];
	return max(
		y&&a[y-1][x]>b?f(y-1,x):0,
		~y+h&&a[y+1][x]>b?f(y+1,x):0,
		x&&a[y][x-1]>b?f(y,x-1):0,
		~x+w&&a[y][x+1]>b?f(y,x+1):0
	)+1;
}
{
	rd(h,w,a(h,w));
	wt(max[y,0,h,x,0,w](f(y,x)));
}