solution: (highlight to read)

1. Rxc7+

from there on white stays on the c-line and cannot lose.

for example

1. Rxc7+ Ka8

2. Rc8+  Kb7

3. Rc7+  Kb6

4. Rc6+  Ka5

5. Rc5+  Ka6

(if 5... Ka4  then 6. Ra5+  K/N xa5   1/2-1/2)

And this goes on until 3 times repetition or the 50 move rule applies.