Join terrain tiles with different height...

I have a big terrain - made in 3DsMax. Because it has more than 2 million vertexes i cannot import it into unity. That's why i separated it into 4 different parts. They all match together in 3dsMax without any problems.

Then i importing files into unity as *.fbx files(each file with number of vertextes below 65K) and using script Object2Terrain - I cannot join terrains anymore. Even if i change terrain height they still do not match. I also using Terrain.SetNeighbors.

Question is how to stitch terrains together without seams?

Here is fbx files: https://www.dropbox.com/s/654t04q5kdhdxa9/terrain2.zip