const fs = require('fs');

Set.prototype.intersect = function(other) {
  let out = new Set();
  other.forEach((entry) => { this.has(entry) && out.add(entry) });
  return out;
}

fs.readFile('input', (err, data) => {
  if (err) throw err;

  let groups = data.toString().split("\n\n").map((group) => {
    let people = group.trim().split("\n").map((person) => new Set(person.trim().split("")));
    return people.reduce((sum,person) => sum.intersect(person));
  });
  
  console.log( groups.reduce((sum, group) => sum + group.size, 0) );
});