#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef int64_t lint;
#define rep(i, n) for(int i=0; i<n; i++)
#define repx(i, l, n) for(int i=l; i<n; i++)
#define all(v) v.begin(), v.end()
#define show(x) cout << #x << ": " << x << endl;
#define list(x) cout << #x << ": " << x << "  ";
#define pb push_back
using vi = vector<lint>;
using vvi = vector<vector<lint>>;
template<class T> inline void vin(vector<T>& v) { rep(i, v.size()) cin >> v.at(i); }
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; }
template<class T> inline void drop(T x) { cout << x << endl; exit(0); }
template<class T> void vout(vector<T> v) { rep(i, v.size()) { cout << v.at(i) << ' '; } cout << endl; }
constexpr lint LINF = LLONG_MAX/2;

int main() {
	lint N, M;
	cin >> N >> M;
	std::vector<string> v(N);
	vin(v);

	lint a=0, b=0, c=0, x, y, z;
	string s = v[0];
	set<string> S;
	rep(i, N) S.insert(v[i]);
	rep(i, M+1) {
		rep(j, 26) {
			if (i != M && j == s[i]-'a') continue;
			x = 'a'+j;
			string t = s.substr(0, i) + char(x) + s.substr(i, M-i);
			bool f = true;
			for (auto u : S) {
				a = 0;
				rep(l, M+1) {
					if (a == M) break;
					if (u[a] == t[l]) a++;
				}
				if (a != M) f = false;
				// if (!f) {list(u) show(t)}
				if (!f) break;
			}
			if (f) c++;
		}
	}
	std::cout << c << '\n';
}