#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define FOR(i, j, k, in) for (int i=j; i<k; i+=in)
#define RFOR(i, j, k, in) for (int i=j; i>=k; i-=in)
#define REP(i, j) FOR(i, 0, j, 1)
#define RREP(i, j) FOR(i, j, 0, 1)
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.end(), a.begin()
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define pii pair<int, int>
#define MOD 1000000007

void solve() {
    ll n, k; cin >> n >> k;
    vector<string> st(n);
    ll m=0;
    REP(i, n) {
        cin >> st[i];
        m = max(m, (ll) st[i].size());
    }
    vector<vector<int>> totals(m, vector<int>(26, 0));
    int s=0, e=0;
    ll total=0, res=0;
    while (true) {
        if (total < k) {
            if (e == n) {
                break;
            }
            REP(i, st[e].size()) {
                total += totals[i][st[e][i] - '0'];
                totals[i][st[e][i] - '0']++;
            }
            e++;
        } else {
            REP(i, st[s].size()) {
                totals[i][st[s][i] - '0']--;
                total -= totals[i][st[s][i] - '0'];
            }
            s++;
            res += n-e+1;
        }
    }
    cout << res << endl;


}

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    ll n=1;
    //  cin >> n;
    REP(i, n) {
        solve();
    }
    return 0;
}