void solve() {
            int n = scanner.nextInt();
            int m = scanner.nextInt();
            long a = scanner.nextInt();
            long b = scanner.nextInt();
            scanner.nextLine();

            // create tree
            int[] parents = new int[n];
            for (int i=1; i<n; i++) {
                int p = scanner.nextInt();
                scanner.nextLine();
                parents[i] = p;
            }

            // mark buyers for each node in tree
            int[] c = new int[n];
            for (int i=0; i<m; i++) {
                long v = (a * i + b) % n;
                c[(int) v]++;
            }

            last = new int[n];
            for (int i=0; i<n; i++) last[i] = i;

            long ans = 0;
            for (int i=n-1; i>=0; i--) {

                // find first grandparent which has buyers available (or possible root with 0 buyers)
                int gp = last[i];
                while (c[gp] == 0 && parents[gp] != gp) gp = parents[gp];

                // speedup future searches by marking this grandparent to all nodes within this path
                int update = last[i];
                while (update != gp) {
                    last[update] = gp;
                    update = parents[update];
                }

                // if grandparent has buyers available, spend 1 buyer on candy i
                if (c[gp] > 0) {
                    c[gp]--;
                    ans += i;
                }
            }

            io.println(ans);
        }