You are given a code:

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

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