cannot insert and save data to a table connected to postgresql on window forms

I cannot insert and save data on a table in my window forms program.

The code on window forms is:

private void BtnInsert_Click(object sender, EventArgs e)
        {
            rowIndex = -1;
            textIdentificacao.Enabled = textNome.Enabled = true;
            textIdentificacao.Text = textNome.Text = null;
            textIdentificacao.Select();

        }


private void BtnSave_Click(object sender, EventArgs e)
        {
            int result = 0;
            if (rowIndex < 0)//insert
            {

                try
                {
                    conn.Open();
                    sql = @"Select * from insert(:_docente_id,:_nome_docente)";
                    cmd = new NpgsqlCommand(sql, conn);
                    cmd.Parameters.AddWithValue("_docente_id", textIdentificacao.Text);
                    cmd.Parameters.AddWithValue("_nome_docente", textNome.Text);                  
                    result = (int)cmd.ExecuteScalar();
                    conn.Close();
                    if (result == 1)
                    {
                        MessageBox.Show("Inserido com sucesso.");
                        Select();
                    }
                    else
                    {
                        MessageBox.Show("Inserção falhou.");
                    }
                }
                catch (Exception ex)
                {
                    conn.Close();
                    MessageBox.Show("Inserção falhou. Error:" + ex.Message);

                }

            }
            result = 0;
            textIdentificacao.Text = textNome.Text = null;
            textIdentificacao.Enabled = textNome.Enabled = false;
        }
    }

the function in posgresql is:

create or replace function insert(_docente_id int, _nome_docente varchar)
returns int as
$$
begin
    insert into docente(docente_id, nome_docente)
    values(_docente_id, _nome_docente);
    if found then
    return 1;
    else return 0;
    end if;
end
$$
language plpgsql

The error is: error 42883 function insert(text, text) does not exist

I think the problem is connected with the int and text. Because the function in postgresql has one int and one varchar and in c# I'm using cmd.Parameters.AddWithValue("_docente_id", textIdentificacao.Text); cmd.Parameters.AddWithValue("_nome_docente", textNome.Text);

Thanks