#include <algorithm>
#include <functional>
#include <iostream>
#include <list>
#include <map>
using namespace std;
#define int long long
signed main () {
ios::sync_with_stdio (false);
cin.tie (0);
cout.tie (0);
int N = 0, K = 0;
cin >> N >> K;
string str = "";
cin >> str;
str = " " + str;
vector <int> nJ (N + 2);
nJ[N] = nJ[N + 1] = N + 1;
for (int i = N - 1; i >= 1; i--)
if (str[i + 1] == 'J')
nJ[i] = i + 1;
else
nJ[i] = nJ[i + 1];
vector <vector <pair <int, int> > > binJ (
N + 2,
vector <pair <int, int> > (20)
);
for (int p = 0; p <= 19; p++)
if (p == 0)
for (int i = N + 1; i >= 1; i--)
binJ[i][0] = {nJ[i], nJ[i] - i - 1};
else
for (int i = N + 1; i >= 1; i--)
binJ[i][p] = {
binJ[
binJ[i][p - 1].first
][p - 1].first,
binJ[i][p - 1].second +
binJ[
binJ[i][p - 1].first
][p - 1].second
};
vector <int> nO (N + 2);
nO[N] = nO[N + 1] = N + 1;
for (int i = N - 1; i >= 1; i--)
if (str[i + 1] == 'O')
nO[i] = i + 1;
else
nO[i] = nO[i + 1];
vector <vector <pair <int, int> > > binO (
N + 2,
vector <pair <int, int> > (20)
);
for (int p = 0; p <= 19; p++)
if (p == 0)
for (int i = N + 1; i >= 1; i--)
binO[i][0] = {nO[i], nO[i] - i - 1};
else
for (int i = N + 1; i >= 1; i--)
binO[i][p] = {
binO[
binO[i][p - 1].first
][p - 1].first,
binO[i][p - 1].second +
binO[
binO[i][p - 1].first
][p - 1].second
};
vector <int> nI (N + 2);
nI[N] = nI[N + 1] = N + 1;
for (int i = N - 1; i >= 1; i--)
if (str[i + 1] == 'I')
nI[i] = i + 1;
else
nI[i] = nI[i + 1];
vector <vector <pair <int, int> > > binI (
N + 2,
vector <pair <int, int> > (20)
);
for (int p = 0; p <= 19; p++)
if (p == 0)
for (int i = N + 1; i >= 1; i--)
binI[i][0] = {nI[i], nI[i] - i - 1};
else
for (int i = N + 1; i >= 1; i--)
binI[i][p] = {
binI[
binI[i][p - 1].first
][p - 1].first,
binI[i][p - 1].second +
binI[
binI[i][p - 1].first
][p - 1].second
};
int actans = 2e9;
for (int i = N - 2; i >= 1; i--)
if (str[i] == 'J') {
int ind = i;
int ans = 0;
for (int p = 19; p >= 0; p--)
if ((K - 1) & (1 << p)) {
ans += binJ[ind][p].second;
ind = binJ[ind][p].first;
}
for (int p = 19; p >= 0; p--)
if (K & (1 << p)) {
ans += binO[ind][p].second;
ind = binO[ind][p].first;
}
for (int p = 19; p >= 0; p--)
if (K & (1 << p)) {
ans += binI[ind][p].second;
ind = binI[ind][p].first;
}
if (ind <= N)
actans = min (actans, ans);
}
if (actans == 2e9)
cout << -1 << '\n';
else
cout << actans << '\n';
}
