const lines = require('fs')
  .readFileSync('/dev/stdin', 'utf-8')
  .trim().split('\n').values();

const N = Number(lines.next().value);
const m = new Map();
let ans = 0;

for (let i = 0; i < N; i++) {
  for (let a of lines.next().value.split(' ')) {
    if (!m.get(a)) {
      m.set(a, 0);
    }
    m.set(a, m.get(a) + 1);
    if (m.get(a) === 2) {
      m.delete(a);
      ans += 1;
    }
  }
}

ans += Math.floor(m.size / 4);

console.log(ans);