#include <iostream>
#include <string>
#include <vector>
#include <cmath>
#include <queue>
#include <utility>
#include <algorithm>

const std::string nucl = "ATGC";

unsigned dist(std::string a, std::string b) {
    unsigned d = 0;
    for (unsigned i = 0; i < a.length(); ++i) {
        unsigned curr = (nucl.find(a[i]) > nucl.find(b[i]) ? nucl.find(a[i]) - nucl.find(b[i]) : nucl.find(b[i]) - nucl.find(a[i]));
        d += std::min(curr, 4 - curr);
    }
    return d;
}

int main() {
    unsigned n, l;
    std::cin >> n >> l;
    std::vector<std::string> acids(n + 1);
    acids[0] = std::string(l, 'A');
    for (unsigned i = 1; i < n + 1; ++i) {
        std::cin >> acids[i];
    }

    std::vector<std::vector<unsigned>> matrix(n + 1, std::vector<unsigned>(n + 1, 0));
    for (unsigned i = 0; i < n + 1; ++i) {
        for (unsigned j = 0; j < n + 1; ++j) {
            matrix[i][j] = dist(acids[i], acids[j]);
        }
    }

    std::vector<bool> used(n + 1, false);
    unsigned mst_weight = 0;
    std::priority_queue<std::pair<int, int>, std::vector<std::pair<int, int>>, std::greater<std::pair<int, int>>> q;
    q.push({0, 0});
    while (!q.empty()) {
        std::pair<int, int> c = q.top();
        q.pop();
        int dst = c.first, v = c.second;
        if (used[v]) {
            continue;
        }
        used[v] = true;
        mst_weight += dst;
        for (unsigned u = 0; u < n + 1; ++u) {
            unsigned len_vu = matrix[v][u];
            if (!used[u]) {
                q.push({len_vu, u});
            }
        }
    }
    std::cout << mst_weight << std::endl;

    return 0;
}