function int readOperation() {
    var int ch;
    let ch = Keyboard.readChar();
    do Output.backSpace();
    if ((ch = 130)) { return 0; }
    if ((ch = 131)) { return 1; }
    if ((ch = 132)) { return 2; }
    if ((ch = 133)) { return 3; }
    return -1;
}
// 130 = left
// 131 = up
// 132 = right
// 133 = down

function void drawCell(int type, int x, int y, int size) {
    var int r, w;
    let r = size / 2;
    let w = 2;
    do Screen.setColor(false);
    do Screen.drawRectangle(x, y, x + size, y + size);
    if (type = PLAYER) {
        do Screen.setColor(true);
        do Screen.drawCircle(x + r, y + r, r);
    }
    if (type = POINT) {
        do Screen.setColor(true);
        do Screen.drawCircle(x + r, y + r, w);
    }
    if (type = NORMAL_BLOCK) {
        do Screen.setColor(true);
        do Screen.drawRectangle(x, y, x + size, y + size);
    }
    if (type = STABLE_BLOCK) {
        do Screen.setColor(true);
        do Screen.drawRectangle(x, y, x + size, y + size);
        do Screen.setColor(false);
        do Screen.drawRectangle(x + w, y + w, x + size - w, y + size - w);
        do Screen.setColor(true);
        do Screen.drawLine(x, y, x + size, y + size);
        do Screen.drawLine(x + size, y, x, y + size);
    }
    return;
}