I saw this puzzle many moons ago and so I assumed it would already be on here somewhere. I have looked and not found, though, and so I present to you a puzzle that baffled me when first I saw it.<br><br>
What number replaces the question mark in the last example and why?

3531 = 0<br>
3597 = 1<br>
3891 = 3<br>
9397 = 2<br>
3869 = 4<br>
2128 = 2<br>
3786 = 3<br>
3506 = 2<br>
2700 = 2<br>
7212 = 0<br>
7205 = 1<br>
2990 = 3<br>
9503 = 2<br>
1057 = 1<br>
1160 = 2<br>

1995 = ?<br>