Balloon Problem

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

import static java.lang.Integer.parseInt;

/**
 * Created by bugkiller on 09/06/19.
 */
class Baloni {

    static int a[] = new int[1000000];
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = parseInt(br.readLine());
        String s[] = br.readLine().split("\\s");
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(s[i]);
        }
        System.out.println(minimumArrows(a, n));
    }

    private static int minimumArrows(int[] a, int n) {
        Map<Integer, Integer> frequency = new HashMap<>();
        int arrows = 0;
        for (int i = 0; i < n; i++) {
            if (frequency.containsKey(a[i])) {
                frequency.compute(a[i], (key, value) -> value - 1);
                frequency.remove(a[i], 0);
                frequency.merge(a[i] - 1, 1, (ov, nv) -> ov + 1);
            } else {
                frequency.merge(a[i] - 1, 1, (ov, nv) -> ov + 1);
                arrows++;
            }
        }
        return arrows;
    }
}