import std.algorithm;
import std.array;
import std.conv;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;

int calc(string a, string b, string c) {
    int n = cast(int) a.length;

    int ans = 0;
    for (int i = 0; i < n; i++) {
        bool[char] d;
        d[a[i]] = true;
        d[b[i]] = true;
        d[c[i]] = true;

        switch (d.keys.length) {
        case 2:
            ans += 1;
            break;
        case 3:
            ans += 2;
            break;
        default:
            break;
        }

    }
    return ans;
}

void main() {
    readint;
    string a = read!string;
    string b = read!string;
    string c = read!string;
    writeln(calc(a, b, c));
}
