#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int n, m; cin >> n >> m;
    vector<string> s(n);
    for(int i = 0; i < n; i++) cin >> s[i];
    auto ok = [&](string t){
        vector<int> indices(n);
        for(int j = 0; j <= m; j++){
            for(int i = 0; i < n; i++){
                if(t[j] == s[i][indices[i]]){
                    indices[i]++;
                }else{
                    if(indices[i] == j-1) return false;
                }
            }
        }
        return true;
    };
    for(int j = 0; j < m; j++){
        vector<int> cnt(26);
        for(int i = 0; i < n; i++){
            cnt[s[i][j]-'a']++;
        }
        int cnt_max = *max_element(cnt.begin(), cnt.end());
        if(cnt_max == n) continue;
        if(cnt_max == n-1){
            int ans = 0;
            for(int i = 0; i < 26; i++){
                if(cnt[i] == 1){
                    int ii = -1;
                    for(int k = 0; k < n; k++) {
                        if(s[k][j]-'a' == i) ii = k;
                    }
                    int jj = (i+1)%n;
                    string t = s[ii].substr(0, j);
                    t += s[jj][j];
                    t += s[ii].substr(j, m-j);
                    // debug_value(t)
                    if(ok(t)) ans++;
                }
            }
            cout << ans << endl;
            return 0;
        }else{
            cout << 0 << endl;
            return 0;
        }
    }
}