'use strict';

function Main(input) {
  const N = Number(input.split("\n")[0]);
  const A = input.split("\n")[1];
  const B = input.split("\n")[2];
  const C = input.split("\n")[3];

  let count = 0;

  for(let i=0; i<N; i++) {
    const a = A.substr(i, 1)
    const b = B.substr(i, 1)
    const c = C.substr(i, 1)
    if ((a === b && a !== c) || (b === c && a !== b) || (a === c && a !== b)) {
      count++;
    }
    if (a !== b && b !== c && c !== a) {
      count += 2;
    }
  }

  console.log(count);

};

Main(require("fs").readFileSync("/dev/stdin", "utf8").trim());
