// IN THE NAME OF ALLAH
// Coded by Ahsanul Imam
#include<bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>order_set;
// find_by_order() - Returns an iterator to the k-th largest element(counting from zero)
// order_of_key() - The number of items in a set that are strictly smaller than our item
typedef long long int ll;
const int  MOD = 1000000007;
#define pb push_back
#define vi vector<int>
#define vl vector<ll>
#define f first
#define s second
#define nl '\n';
#define bit(a) __builtin_popcountll(a)
#define cnt_sese_sunno(x) __builtin_ctz(x)
#define cnt_age_sunno(x) __builtin_clz(x)
#define cnt_sese_ek(x) __builtin_ctz(~x)
#define cnt_age_ek(x) __builtin_clz(~x)
#define parity(x) __builtin_parity(x)
#define parityLL(x) __builtin_parityll(x)
#define w(x) while (x--)
#define test int t; cin>>t; for (int i = 1; i <= t; i++)
#define loop for (int i = 0; i < n; i++)
#define print(v) for(auto it:v)cout<<it<<' ';cout<<endl;
#define srt(v) sort(v.begin(), v.end());
#define rsrt(v) sort(v.rbegin(), v.rend());
#define gcd(a, b) __gcd<long long int>(a, b)
#define lcm(a, b) (a * b) / gcd(a, b)
#define pi 2*acos(0.0)
#define pr pair<int, int>
#define Ahsanul (ios_base::sync_with_stdio(false), cin.tie(NULL))
vector<pr>knight_posible{{2, 1}, {2, -1}, {1, 2}, {1, -2}, {-1, 2}, {-1, -2}, {-2, 1}, {-2, -1}};//knight moves
vector<pr>posible{{0,-1},{0,1},{-1,0},{1,0},{-1,-1},{-1,1},{1,-1},{1,1}};//eight direction moves;
int power(int a,int b){int res=1;while (b){if (b&1){res=(res*1ll*a)%MOD;}a=(a*1ll*a)%MOD;b>>=1;}return res;}
ll inversemod(ll base) { return power(base,MOD-2); }
void solve()
{
    int n,k; cin>>n>>k;
    string s; cin>>s;
    int j=0;
    for(int i=0;i<=n-k;i++)
    {
        char last=s[i];int idx=i;
        if(i==n-k)
        {
            sort(s.begin()+i,s.end());
            break;
        }
        while(abs(i-j)<k)
        {
            if(s[j]<last)
            {
                last=s[j];
                idx=j;
            }
            j++;
        }
        //cout<<i<<' '<<mini<<' '<<idx<<' '<<j<<nl;
        if(idx==i)
        {
            continue;
        }
        else
        {
            sort(s.begin()+i,s.begin()+i+k);
            i+=k-1;
        }
    }
    cout<<s<<nl;
}
int main()
{
    Ahsanul;
    //test
    {
        //cout<<"Case "<<i<<": ";
        solve();
    }
}