File status 35 - what did I do wrong?

OPEN INPUT fails with file status 35. Program compiles. JCL looks ok to me. What does 35 mean in beginner terms?

35 = file not found at OPEN. Usually the DD is missing, the DD name does not match ASSIGN, or the DSN is misspelled / not cataloged.

Check SELECT ASSIGN name vs //DDNAME in JCL character by character. Also confirm the dataset exists in 3.4.

DD was INPUT1 in JCL and INPUT01 in the program. Classic. Fixed.