#include <bits/stdc++.h>
#define fr first
#define sc second
#define pii pair<int, int>
#define pb push_back
#define szof(s) (int)s.size()
#define all(s) s.begin(), s.end()
#define fastInp ios_base::sync_with_stdio(0); cin.tie(0);
using namespace std;
const int INF = 1e9;
const int MAXN = (int)2e5 + 5;
vector <char> vec = {'J', 'O', 'I', '#'};
int cnt[1000];
int pref[MAXN][3];
int n, k;
string s;
int f(char c) {
if (c == 'J') {
return 0;
}
if (c == 'O') {
return 1;
}
if (c == 'I') {
return 2;
}
}
int get_cnt(int l, int r, int type) {
if (l > r) {
return 0;
}
if (l == 0) {
return pref[r][type];
} else {
return pref[r][type] - pref[l - 1][type];
}
}
int find_pos(int l, int r, char ch, int k) {
if (get_cnt(l, r, f(ch)) >= k) {
int bl = l - 1, br = r;
while (br - bl > 1) {
int bmid = (bl + br) >> 1;
if (get_cnt(l, bmid, f(ch)) >= k) {
br = bmid;
} else {
bl = bmid;
}
}
return br;
} else {
return -1;
}
}
bool can(int l, int r, int k) {
int opt_j = find_pos(l, r, 'J', k);
if (opt_j == -1) {
return false;
}
int opt_o = find_pos(opt_j + 1, r, 'O', k);
if (opt_o == -1) {
return false;
}
int opt_i = find_pos(opt_o + 1, r, 'I', k);
if (opt_i == -1) {
return false;
}
return true;
}
signed main() {
fastInp;
cin >> n >> k;
cin >> s;
for (int i = 0; i < n; i++) {
if (i > 0) {
for (int j = 0; j < 3; j++) {
pref[i][j] = pref[i - 1][j];
}
}
pref[i][f(s[i])]++;
}
int ans = INF;
for (int l = 0; l < n; l++) {
if (can(l, n - 1, k)) {
int bl = l, br = n - 1;
while (br - bl > 1) {
int bmid = (bl + br) >> 1;
if (can(l, bmid, k)) {
br = bmid;
} else {
bl = bmid;
}
}
ans = min(ans, (br - l + 1) - k * 3);
}
}
if (ans == INF) {
ans = -1;
}
cout << ans << endl;
}
/*
10 2
OJIJOIOIIJ
*/
