#include <bits/stdc++.h>
#include <experimental/random>
#include <random>
using namespace std;
using ll = long long;
using ld = long double;
const ll INF = 1e18, MOD = 998244353;
void solve();
signed main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
ll q = 1;
//cin >> q;
while (q--) {
solve();
}
}
void solve() {
ll n, k;
cin >> n >> k;
string s;
cin >> s;
string t;
for (int i = 0; i < k; i++) {
t += 'J';
}
for (int i = 0; i < k; i++) {
t += 'O';
}
for (int i = 0; i < k; i++) {
t += 'I';
}
ll ans = INF;
for (int st = 0; st < n; st++) {
if (s[st] != 'J') {
continue;
}
ll idx = 0, i = st, cnt = 0;
while (idx < t.size() && i < s.size()) {
if (s[i] != t[idx]) {
cnt++;
} else {
idx++;
}
i++;
}
if (idx == t.size()) {
ans = min(ans, cnt);
}
}
if (ans == INF) {
cout << -1;
} else {
cout << ans;
}
}
