#include <bits/stdc++.h>
using namespace std;
const int inf = 1e9;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n, k;
cin >> n >> k;
string s;
s.resize(n + 1);
for (int i = 1; i <= n; ++i) cin >> s[i];
vector<int> posj, poso, posi;
for (int i = 1; i <= n; ++i) {
if (s[i] == 'J') posj.push_back(i);
else if (s[i] == 'O') poso.push_back(i);
else if (s[i] == 'I') posi.push_back(i);
}
int res = inf;
for (int i = 1; i <= n; ++i) {
int curpos = i - 1;
int idx = (int)(lower_bound(posj.begin(), posj.end(), curpos + 1) - posj.begin());
if (idx + k - 1 >= (int)posj.size()) continue;
curpos = posj[idx + k - 1];
idx = (int)(lower_bound(poso.begin(), poso.end(), curpos + 1) - poso.begin());
if (idx + k - 1 >= (int)poso.size()) continue;
curpos = poso[idx + k - 1];
idx = (int)(lower_bound(posi.begin(), posi.end(), curpos + 1) - posi.begin());
if (idx + k - 1 >= (int)posi.size()) continue;
curpos = posi[idx + k - 1];
res = min(res, curpos - i + 1 - 3 * k);
}
if (res == inf) cout << "-1\n";
else cout << res << "\n";
return 0;
}
