#pragma region macro
#include <bits/stdc++.h>
using i64 = int_fast64_t;
#define repeat(i, a, b) for(int i = (a); (i) < (b); ++(i))
#define rep(i, n) repeat(i, 0, n)

namespace std {
template <typename A, typename B>
string to_string(pair<A, B> p);

string to_string(const string& s) {
    return '"' + s + '"';
}

string to_string(const char* s) {
    return to_string((string)s);
}

string to_string(bool b) {
    return (b ? "true" : "false");
}

string to_string(vector<bool> v) {
    bool first = true;
    string res = "{";
    for(int i = 0; i < static_cast<int>(v.size()); i++) {
        if(!first) {
            res += ", ";
        }
        first = false;
        res += to_string(v[i]);
    }
    res += "}";
    return res;
}

template <size_t N>
string to_string(bitset<N> v) {
    string res = "";
    for(size_t i = 0; i < N; i++) {
        res += static_cast<char>('0' + v[i]);
    }
    return res;
}

template <typename A>
string to_string(A v) {
    bool first = true;
    string res = "{";
    for(const auto& x : v) {
        if(!first) {
            res += ", ";
        }
        first = false;
        res += to_string(x);
    }
    res += "}";
    return res;
}

template <typename A, typename B>
string to_string(pair<A, B> p) {
    return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
};  // namespace std

namespace edamat {
// modint: mod 計算を int を扱うように扱える構造体
template <int MOD>
struct Fp {
    int_fast64_t val;
    constexpr Fp(int_fast64_t v = 0) noexcept : val(v % MOD) {
        if(val < 0) val += MOD;
    }
    constexpr int getmod() { return MOD; }
    constexpr Fp operator-() const noexcept {
        return val ? MOD - val : 0;
    }
    constexpr Fp operator+(const Fp& r) const noexcept { return Fp(*this) += r; }
    constexpr Fp operator-(const Fp& r) const noexcept { return Fp(*this) -= r; }
    constexpr Fp operator*(const Fp& r) const noexcept { return Fp(*this) *= r; }
    constexpr Fp operator/(const Fp& r) const noexcept { return Fp(*this) /= r; }
    constexpr Fp& operator+=(const Fp& r) noexcept {
        val += r.val;
        if(val >= MOD) val -= MOD;
        return *this;
    }
    constexpr Fp& operator-=(const Fp& r) noexcept {
        val -= r.val;
        if(val < 0) val += MOD;
        return *this;
    }
    constexpr Fp& operator*=(const Fp& r) noexcept {
        val = val * r.val % MOD;
        return *this;
    }
    constexpr Fp& operator/=(const Fp& r) noexcept {
        int_fast64_t a = r.val, b = MOD, u = 1, v = 0;
        while(b) {
            int_fast64_t t = a / b;
            a -= t * b;
            std::swap(a, b);
            u -= t * v;
            std::swap(u, v);
        }
        val = val * u % MOD;
        if(val < 0) val += MOD;
        return *this;
    }
    constexpr bool operator==(const Fp& r) const noexcept {
        return this->val == r.val;
    }
    constexpr bool operator!=(const Fp& r) const noexcept {
        return this->val != r.val;
    }
    friend constexpr std::ostream& operator<<(std::ostream& os, const Fp<MOD>& x) noexcept {
        return os << x.val;
    }
    friend constexpr std::istream& operator>>(std::istream& is, Fp<MOD>& x) noexcept {
        return is >> x.val;
    }
    friend constexpr Fp<MOD> modpow(const Fp<MOD>& a, int_fast64_t n) noexcept {
        if(n == 0) return 1;
        auto t = modpow(a, n / 2);
        t = t * t;
        if(n & 1) t = t * a;
        return t;
    }
};

// 二項係数ライブラリ
template <class T>
struct BiCoef {
    std::vector<T> fact_, inv_, finv_;
    constexpr BiCoef() {}
    constexpr BiCoef(int n) noexcept : fact_(n, 1), inv_(n, 1), finv_(n, 1) {
        init(n);
    }
    constexpr void init(int n) noexcept {
        fact_.assign(n, 1), inv_.assign(n, 1), finv_.assign(n, 1);
        int MOD = fact_[0].getmod();
        for(int i = 2; i < n; i++) {
            fact_[i] = fact_[i - 1] * i;
            inv_[i] = -inv_[MOD % i] * (MOD / i);
            finv_[i] = finv_[i - 1] * inv_[i];
        }
    }
    constexpr T com(int n, int k) const noexcept {
        if(n < k || n < 0 || k < 0) return 0;
        return fact_[n] * finv_[k] * finv_[n - k];
    }
    constexpr T fact(int n) const noexcept {
        if(n < 0) return 0;
        return fact_[n];
    }
    constexpr T inv(int n) const noexcept {
        if(n < 0) return 0;
        return inv_[n];
    }
    constexpr T finv(int n) const noexcept {
        if(n < 0) return 0;
        return finv_[n];
    }
};
}  // namespace edamat

const int MOD = 1000000007;
using modint = edamat::Fp<MOD>;
edamat::BiCoef<modint> bc;

#pragma endregion

void solve() {
    int n;
    std::string a, b, c;
    std::cin >> n;
    std::cin >> a >> b >> c;
    int ans = 0;
    rep(i, n) {
        if(a[i] == b[i] and b[i] != c[i]) {
            ans++;
        } else if(b[i] == c[i] and b[i] != a[i]) {
            ans++;
        } else if(a[i] == c[i] and a[i] != b[i]) {
            ans++;
        } else if(a[i] == b[i] and b[i] == c[i]) {
            continue;
        } else {
            ans += 2;
        }
    }
    std::cout << ans << std::endl;
}

int main() {
    // std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    solve();
    return 0;
}

Measured memory_bytes: 256