#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int N = 2e5 + 24;
int n, k; string s;
int pf[N][3];
void solve() {
cin >> n >> k;
cin >> s; s = "." + s;
for (int i = 1; i <= n; i++) {
pf[i][0] = pf[i - 1][0] + (s[i] == 'J');
pf[i][1] = pf[i - 1][1] + (s[i] == 'O');
pf[i][2] = pf[i - 1][2] + (s[i] == 'I');
}
int res = -1;
for (int i = 1; i <= n; i++) {
int pos = i; bool flag = 0;
for (int j = 0; j < 3; j++) {
int next_pos = -1;
for (int l = pos, r = n; l <= r; ) {
int mid = (l + r) / 2;
if (pf[mid][j] - pf[pos - 1][j] >= k) {
next_pos = mid;
r = mid - 1;
}
else l = mid + 1;
}
if (next_pos == -1) {
flag = 1; break;
}
pos = next_pos;
}
if (!flag && (res == -1 || res > (pos - i + 1) - 3 * k)) {
res = (pos - i + 1) - 3 * k;
}
}
cout << res << '\n';
}
int main() {
cin.tie(0) -> sync_with_stdio(0);
int T = 1; // cin >> T;
while (T--) {
solve();
}
}
