#include "bits/stdc++.h"
using namespace std;
using ll = long long;
using pii = pair<int, int>;
int c2i(char c) {
if (c == 'J') return 0;
else if (c == 'O') return 1;
else return 2;
}
int main() {
cin.tie(0)->sync_with_stdio(0);
int n, k;
string s;
cin >> n >> k;
vector p = vector(n + 5, vector<int>(3, 0));
cin >> s;
for (int i = 0; i < n; i++) {
if (i > 0) {
for (int k = 0; k < 3; k++) {
p[i][k] = p[i - 1][k];
}
}
++p[i][c2i(s[i])];
}
auto rge_sum = [&](int l, int r, char c) {
int ret = p[r][c2i(c)];
if (l > 0) {
ret -= p[l - 1][c2i(c)];
}
return ret;
};
int ans = -1;
int jen = 0;
int oen = 0;
int ien = 0;
for (int i = 0; i < n; i++) {
if (jen < i) jen = i;
while (jen < n && rge_sum(i, jen, 'J') < k) {
++jen;
}
if (jen == n && rge_sum(i, jen, 'J') < k) break;
if (oen <= jen) oen = jen + 1;
while (oen < n && rge_sum(jen + 1, oen, 'O') < k) {
++oen;
}
if (oen == n && rge_sum(jen + 1, oen, 'O') < k) break;
if (ien <= oen) ien = oen + 1;
while (ien < n && rge_sum(oen + 1, ien, 'I') < k) {
++ien;
}
if (ien == n && rge_sum(oen + 1, ien, 'I') < k) break;
int cost = ien - i + 1 - 3 * k;
if (ans == -1 || cost < ans) ans = cost;
}
cout << ans << endl;
}
