You are given a code:

def main_solution(x):
    return func_13(('ptgbzr' + 'ewryky'), '_')

Can you predict the output of `main_solution("sisprvvmx")` 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": "sisprvvmx"}, "ref_output": "p_t_g_b_z_r_e_w_r_y_k_y", "ref_code": "def main_solution(x):\n    return func_13(('ptgbzr' + 'ewryky'), '_')", "funcname": "main_solution"}
rule