[CrazY.]

#include <amxmodx>
#include <amxmisc>

public plugin_init()
{
    register_plugin("Plugin", "Version", "Author")

    new filename[128]
    formatex(filename[get_configsdir(filename, charsmax(filename))], charsmax(filename), "/numbers.txt")
    new file = fopen(filename, "r+t")

    if (file)
    {
        new buffer[15]
        new num = 0

        if (fgets(file, buffer, charsmax(buffer)))
            num = str_to_num(buffer[1]) + 1

        fseek(file, 0, SEEK_SET)
        fprintf(file, "A%d", num)

        fclose(file)
    }
}