#include <bits/stdc++.h>
using namespace std;
using ll=long long;
#define all(x) (x).begin(), (x).end()

const int N=3e5+5;
int v[N], t[N][26];
int tot=1;
void insert(string s)
{
    int p=1;
    for(int i=0;i<s.size();++i)
    {
        int x=s[i]-'a';
        if(t[p][x]==0) t[p][x]=++tot;
        p=t[p][x];
    }
    v[p]++;
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    
    int n, k;
    cin>>n>>k;
    for(int i=1;i<=n;++i)
    {
        string s;
        cin >> s;
        insert(s);
    }
    
    
    function<int(int)> dfs=[&](int x) -> int
    {
        int cnt=0;
        vector<int> val; int sm=0;
        for(int i=0;i<26;++i) if(t[x][i]) cnt+=dfs(t[x][i]), val.push_back(v[t[x][i]]), sm+=v[t[x][i]];
        sort(all(val));
        if(sm+v[x]>k)
        {
            while(sm+v[x]>k)
            {
                assert(val.size());
                sm-=val.back();
                ++cnt;
                val.pop_back();
            }
        }
        v[x]+=sm;
        assert(v[x]<=k);
        if(x==1 && v[x]) v[x]=0, ++cnt;
        return cnt;
    };
    
    cout << dfs(1) << "\n";
}