Put both hands and both knees on the floor. Lean forward a bit and raise your feet.
Now slowly start moving with your arms forward in front of you, stretching your body into a straight position except of your knees that remains bent. Go down as far as you can without touching the floor with your body. Breathe in during this portion of the movement.
After a pause at the stretched position, start pulling yourself back to the starting position as you breathe out. Go slowly and keep your abs tight at all times.