import std.stdio, std.string, std.conv;
import std.algorithm, std.array, std.range;
auto solve(string S_) {
    immutable N=S_.chomp.to!int();
    immutable A=readln.chomp();
    immutable B=readln.chomp();
    immutable C=readln.chomp();
    int k=0;
    foreach(i;0..N) {
        if(A[i]!=B[i]) {
            ++k;
            if(A[i]!=C[i] && B[i]!=C[i]) ++k;
        }
        else if(B[i]!=C[i]) {
            ++k;
        }
    }
    return k;
}
void main(){ for(string s; (s=readln.chomp()).length;) writeln(solve(s)); }