You are given a code:

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

Can you predict the output of `main_solution("yxbtfnfirz")` 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": "yxbtfnfirz"}, "ref_output": "l_i_g_a_j_u_y_x_b_t_f_n_f_i_r_z", "ref_code": "def main_solution(x):\n    return func_13(('ligaju' + x), '_')", "funcname": "main_solution"}
rule