#include <iostream>
#include <iomanip>
#include <random>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <numeric>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <sstream>
#include <bitset>
#include <cassert>
#include <fstream>
#include <queue>
#include <stack>
#include <unordered_map>
#include <unordered_set>
#include <limits>

#define len(X) ((int)(X).size())

#ifdef __LOCAL
#define DBG(X) cout << #X << "=" << (X) << '\n';
#define SAY(X) cout << (X) << '\n';
#else
#define DBG(X)
#define SAY(X)
#endif

#define M_PI       3.14159265358979323846

using namespace std;

using ll = long long int;
using ull = unsigned long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

const int INT_INF = (int)(2e9);
const ll  LL_INF = (ll)(2e18);

const int NIL = -1;
static mt19937 _g(time(nullptr));

inline ll randint(ll a, ll b) { ll w = (_g() << 31LL) ^ _g(); return a + w % (b - a + 1); }
inline void fast_io() { ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); };
template<typename T> inline T sign(T x) { return T(x > 0) - T(x < 0); }
template<typename T, typename S> inline ostream& operator<<(ostream& os, const pair<T, S> p) { cout << "[" << p.first << ";" << p.second << "]"; return os; }
template<typename T> inline ostream& operator<<(ostream& os, const vector<T>& v) { for (auto el : v) cout << el << " "; return os; }
template<typename T> inline T fetch() { T ret; cin >> ret; return ret; }
template<typename T> inline vector<T> fetch_vec(int sz) { vector<T> ret(sz); for (auto& elem : ret) cin >> elem; return ret; }

bool topologicalSort(int node, unordered_map<int,
                     vector<int>>& adjs,
                     unordered_set<int>& visited,
                     unordered_set<int>& back,
                     stack<int>& st)
{
    visited.insert(node);
    back.insert(node);

    for (auto& adj : adjs[node])
    {
        if (back.count(adj) != 0) return false;

        if (visited.count(adj) == 0 && !topologicalSort(adj, adjs, visited, back, st))
            return false;
    }

    st.push(node);

    back.erase(node);

    return true;
}

int maxDFS(int node,
    unordered_map<int, vector<int>>&adjs,
    unordered_set<int>& visited,
    unordered_set<int>& back)
{
    visited.insert(node);
    back.insert(node);

    int depth = 0;

    for (auto& adj : adjs[node])
    {
        if (back.count(adj) != 0) return -1;

        if (visited.count(adj) == 0)
        {
            int currDepth = maxDFS(adj, adjs, visited, back);
            if (currDepth == -1)
                return -1;

            depth = std::max(currDepth, depth);
        }
    }

    back.erase(node);

    return 1 + depth;
}

int solve()
{
    int N;
    string s, r, t;

    std::cin >> N;
    std::cin >> s >> r >> t;

    int counter = 0;
    for (int i = 0; i < N; ++i)
    {
        if (s[i] == r[i] && r[i] == t[i])
            continue;

        if (s[i] != r[i] && r[i] != t[i] && s[i] != t[i])
            counter += 2;
        else
            counter += 1;
    }

    return counter;
}

int main()
{
    std::cout << solve() << std::endl;

    return 0;
}


Measured memory_bytes: 256