// O O O O O O O O O O O O O O O OO O OO O OO O O O TTCH O TTTCH O TTTCH O O O O
#pragma GCC optimize("Ofast")
#pragma GCC optimize("no-stack-protector")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("fast-math")
#pragma GCC target("sse,sse2,sse3,ssse3,popcnt,abm,mmx")
#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <stdio.h>
#include <cstdio>
#include <math.h>
#include <cmath>
#include <string>
#include <cstring>
#include <queue>
#include <deque>
// #include <random>
#include <iomanip>
#include <bitset>
#include <cassert>
using namespace std;
#define y1 y11
#define double long double
#define less less228
#define left left228
#define right right228
#define list list228
template<typename T> void uin(T &a, T b) {
if (b < a) a = b;
}
template<typename T> void uax(T &a, T b) {
if (b > a) a = b;
}
// random_device rnd;
// template<typename T> void shuffle(vector< T > &v) {
// for (int i = 1; i < (int)v.size(); ++i) {
// swap(v[rnd() % i], v[i]);
// }
// for (int i = (int)v.size() - 1; i; --i) {
// swap(v[rnd() % i], v[i]);
// }
// }
const int N = 200 * 1000 + 228;
const int LG = 20;
int s[N], last[3];
int p[N][3][LG];
signed main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int n, K;
cin >> n >> K;
for (int i = 1; i <= n; ++i) {
char c;
cin >> c;
if (c == 'J') {
s[i] = 0;
} else if (c == 'O') {
s[i] = 1;
} else {
s[i] = 2;
}
}
last[0] = last[1] = last[2] = n + 1;
for (int j = 0; j < 3; ++j) {
for (int k = 0; k < 20; ++k) {
p[n + 1][j][k] = n + 1;
}
}
for (int i = n; i; --i) {
for (int j = 0; j < 3; ++j) {
p[i][j][0] = last[j];
for (int k = 1; k < LG; ++k) {
p[i][j][k] = p[p[i][j][k - 1]][j][k - 1];
}
}
last[s[i]] = i;
}
int answer = n + 1;
for (int i = 1; i <= n; ++i) {
int pos = i;
for (int j = 0; j < 3; ++j) {
int curK = K;
if (s[pos] == j) curK--;
for (int t = 0; t < LG; ++t) {
if ((curK >> t) & 1) {
pos = p[pos][j][t];
}
}
}
if (pos == n + 1) continue;
uin(answer, pos - i + 1 - 3 * K);
}
if (answer == n + 1) answer = -1;
cout << answer << '\n';
return 0;
}
// RU_023
//
// OJIJOIOIIJ
