**The Best Solution Without Object OverHead from Hash DS. **

import java.util.Scanner;

public class Main{ public static void main(String[] args) { Scanner scan = new Scanner(System.in); int n = scan.nextInt();

    BitSet bset = new BitSet(100);
    int count = 0;

    for(int i = 0; i < n; i++) {
        int num = scan.nextInt();
        //if toggled on
        if(bset.get(num)) {
            count++;
            bset.clear(num);
        }else {
            bset.set(num);
        }
    }

    System.out.println(count);
    scan.close();
}

}

class BitSet{ private long[] bits; private int size;

public BitSet(int size) {
    this.size = size;
    this.bits = new long[(size + 64) / 64];
}

public BitSet() {
    this(64);
}

public void set(int index) {
    if(index < 0) {
        throw new IndexOutOfBoundsException("index must be > 0");
    }else if(index > size) {
        resize(index);
    }

    bits[index / 64] |= (1L << (index % 64));
}

public boolean get(int index) {
    if(index < 0 || index > size) {
        throw new IndexOutOfBoundsException("Index must be > 0 & < size");
    }

    return (bits[index / 64] & (1L << (index % 64))) != 0;
}

public void clear(int index) {
    if(index < 0 || index > size) {
        throw new IndexOutOfBoundsException("Index must be > 0 & < size");
    }

    bits[index / 64] &= ~(1L << (index % 64));
}

public int size() {
    return size;
}

private void resize(int index) {
    long[] newBits = new long[(index + 64) / 64];
    System.arraycopy(bits, 0, newBits, 0, bits.length);
    bits = newBits;
    size = index;
}

}