What is the reason why my code can't do 1000+ input lines?

Question

"Test: #6, time: 62 ms., memory: 228 KB, exit code: 3, checker exit code: 0, verdict: RUNTIME_ERROR Input 1000 R621C406 ABD815 R3C24 R634C162 R695C621 R875C898 AHG626 A