#include <bits/stdc++.h>
using namespace std;
const int INF = (int) 1e9;
int cnt[3];
int n, k;
string s;
int getcost(int x) {
cnt[0] = cnt[1] = cnt[2] = 0;
int cost = 0;
while (x <= n) {
int where = -1;
if (s[x] == 'J') {
where = 0;
} else if (s[x] == 'O') {
where = 1;
} else {
where = 2;
}
int mn = INF;
for (int i = where - 1; i >= 0; i--) {
mn = min(mn, cnt[i]);
}
if (mn < k || cnt[where] == k) {
cost++;
} else {
cnt[where]++;
}
if (cnt[0] == k && cnt[1] == k && cnt[2] == k) {
break;
}
x++;
}
if (cnt[0] != k || cnt[1] != k || cnt[2] != k) {
cost = INF;
}
return cost;
}
signed main() {
ios::sync_with_stdio(0); cin.tie(0);
// freopen("input", "r", stdin);
cin >> n >> k >> s;
s = "#" + s;
int sol = INF;
for (int i = 1; i <= n; i++) {
sol = min(sol, getcost(i));
}
if (sol == INF) {
cout << "-1";
return 0;
}
cout << sol << "\n";
return 0;
}
