You are given a code:

def main_solution(x):
    return (func_13(x, '_') + ('ytpdyy' + 'gjfly'))

Can you predict the output of `main_solution("zzfjwvzk")` without writing any code? Please reason and put your final answer in the following json format: {"output": <your output>}, where <your output> should be the final string.
user
{"ref_input": {"x": "zzfjwvzk"}, "ref_output": "z_z_f_j_w_v_z_kytpdyygjfly", "ref_code": "def main_solution(x):\n    return (func_13(x, '_') + ('ytpdyy' + 'gjfly'))", "funcname": "main_solution"}
rule