Task: Program Execution
Input (English): 1, 3, ['6539', 'x', 'P', '9989', 'Z', '7297', '7637', 'U', '8235', '2631', 'x', '2031', 'R', 'C', 'b', 'J', 'b', '7735', 'z', 'M']
Output (English): P, x, 6539