"use strict";
function Main(input) {
    var lines = input.split("\n");
    var N = lines.shift() - 0;
    var strA = lines[0];
    var strB = lines[1];
    var strC = lines[2];
    var count = 0;
    var match = new Array(N).fill(0);
    for (var n = 0; n < N; n++) {
        if (strA.charAt(n) == strB.charAt(n)) {
            if (strA.charAt(n) == strC.charAt(n)) {
                match[n] = 3;
            } else {
                match[n] = 2;
            }
        } else if (strB.charAt(n) == strC.charAt(n)) {
            match[n] = 2;
        } else if (strA.charAt(n) == strC.charAt(n)) {
            match[n] = 2;
        } 
    }
    for (var n = 0; n < N; n++) {
        switch (match[n]) {
        case 3:
            break;
        case 2:
            count += 1;
            break;
        case 1:
        case 0:
            count += 2;
            break;
        }
    }
    console.log(count);
}

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