int read() {
    int res = 0;
    char c = getchar();
    while(!isdigit(c)) c = getchar();
    while(isdigit(c)) res = (res << 1) + (res << 3) + c - 48, c = getchar();
    return res;
}
void write(int x) {
    if(x / 10) write(x / 10);
    putchar(x % 10 + '0');
}