let a = Array.from(new Array(10)).fill(0)
let i = require('fs').readFileSync('/dev/stdin', 'utf8').split('\n').slice(1,-1)
i.forEach((s) => { s.split(' ').forEach((e) => a[e-1]++) })
let u = 0
let d = 0
a.forEach((e) => {
  u += e / 2 | 0
  d += e % 2
})
console.log(u + (d / 4 | 0))