require('fs').readFile('/dev/stdin', 'utf-8', (err, data) => {
  let [n, a, b, c] = data.split('\n');
  let answer = 0;
  for (let i = 0; i < n; i++) {
    if (a[i] === b[i]) {
      if (a[i] !== c[i]) {
        answer++;
      }
    } else {
      if (a[i] === c[i]) {
        answer++;
      } else if (b[i] === c[i]) {
        answer++;
      } else {
        answer += 2;
      }
    }
  }
  console.log(answer);
});