You are given a code:

def main_solution(x):
    return (func_20('bltfur', x) + func_13(x, '_'))

Can you predict the output of `main_solution("vwycpsrlbs")` 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": "vwycpsrlbs"}, "ref_output": "bvlwtyfcuprsrlbsv_w_y_c_p_s_r_l_b_s", "ref_code": "def main_solution(x):\n    return (func_20('bltfur', x) + func_13(x, '_'))", "funcname": "main_solution"}
rule