boolean isGameOver = false;
int turn = 0;
System.out.println("Turns for " + numPlayers + " players:");
do {
    for(int i = 1; i <= numPlayers; i++) {
        turn++;
        System.out.println("Turn " + turn + " --> Player " + i);
        if(turn==20) {
            isGameOver = true;
            break;
        }
    }
    System.out.println("---");
} while (!isGameOver);