function main(input) {
  const data = input.trim().split('\n');
  const abc = data
    .slice(1)
    .map((e) => e.split(' '))
    .flat()
    .map(Number);
  const count = Array(10).fill(0);
  abc.forEach((e) => {
    count[e - 1] += 1;
  });
  let pwup = 0;
  count.forEach((cnt, i) => {
    pwup += Math.floor(cnt / 2);
    count[i] = cnt % 2;
  });
  pwup += Math.floor(count.reduce((acc, e) => acc + e, 0) / 4);
  return pwup;
}

console.log(main(require('fs').readFileSync('/dev/stdin', 'utf8')));