function main(input){
  var n = parseInt(input[0]);
  var a = input[1];
  var b = input[2];
  var c = input[3];
  
  var ans = 0;
  for (var i = 0; i < n; i++){
    var map = {};
    map[a[i]] = 1;
    map[b[i]] = 1;
    map[c[i]] = 1;
    ans += Object.keys(map).length - 1;
  }
  console.log(ans);
}

var input = '';

process.stdin.resume();
process.stdin.setEncoding('utf8');
process.stdin.on('data', function(chunk) {
  input += chunk;
});
process.stdin.on('end', function() {
  input = input.split('\n');
  main(input);
});
