#include <bits/stdc++.h>
#include <vector>
#include <algorithm>
using namespace std;
int main() {
int N, K;
string S;
cin >> N >> K >> S;
// Store positions of J, O, and I
vector<int> J_pos, O_pos, I_pos;
for (int i = 0; i < N; i++) {
if (S[i] == 'J') J_pos.push_back(i);
else if (S[i] == 'O') O_pos.push_back(i);
else if (S[i] == 'I') I_pos.push_back(i);
}
// Check if it's even possible to have K J's, K O's, and K I's
if (J_pos.size() < K || O_pos.size() < K || I_pos.size() < K) {
cout << -1 << endl;
return 0;
}
// Minimize Operation 3 deletions
int min_operations = INT_MAX;
// Iterate over valid JOI segments
for (int j = 0; j <= J_pos.size() - K; j++) {
int start_J = J_pos[j];
int end_J = J_pos[j + K - 1];
auto it_O = lower_bound(O_pos.begin(), O_pos.end(), end_J);
if (it_O == O_pos.end() || distance(it_O, O_pos.end()) < K) continue;
int start_O = *it_O;
int end_O = O_pos[it_O - O_pos.begin() + K - 1];
auto it_I = lower_bound(I_pos.begin(), I_pos.end(), end_O);
if (it_I == I_pos.end() || distance(it_I, I_pos.end()) < K) continue;
int start_I = *it_I;
int end_I = I_pos[it_I - I_pos.begin() + K - 1];
// Calculate operations
int operations = (start_J) + (N - 1 - end_I) +
(start_O - end_J - 1) +
(start_I - end_O - 1);
min_operations = min(min_operations, operations);
}
// Output the result
if (min_operations == INT_MAX) {
cout << -1 << endl;
} else {
cout << min_operations << endl;
}
return 0;
}
