#include "bits/stdc++.h"
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx,avx2,fma")
using namespace std;
#define vec vector
#define int long long
#define inf 1e18
const int mod = 998244353 , men = 1e9 + 7;
/*
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*/
template<typename _T>
bool chmin(_T &a, const _T &b) {
if (a > b) {
a = b;
return true;
}
return false;
}
template <typename _T>
bool chmax(_T &a, const _T &b) {
if (a < b) {
a = b;
return true;
}
return false;
}
double dist(double x1 , double y1 , double x2 , double y2){
return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}
inline void io(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
}
inline void solve(){
int n , k;
cin >> n >> k;
string s;
cin >> s;
int ans = 1e9;
auto tuura = [&](int l , int r){
string c = "";
int jj = k , oo = k , ii = k;
for (int i = l; i <= r; i++){
if (jj > 0 and s[i] == 'J')
c += s[i] , jj--;
if (jj == 0 && oo > 0 && s[i] == 'O')
c += s[i] , oo--;
if (jj == 0 && oo == 0 && ii > 0 && s[i] == 'I')
c += s[i] , ii--;
}
if ((int)c.size() != k * 3 || jj > 0 || oo > 0 || ii > 0)
return false;
for (int i = 0; i < k; i++)
if (c[i] != 'J')
return false;
for (int i = k; i < 2 * k; i++)
if (c[i] != 'O')
return false;
for (int i = 2 * k; i < 3 * k; i++)
if (c[i] != 'I')
return false;
return true;
};
for (int l = 0; l + k - 1 < n; l++){
for (int r = l + k - 1; r < n; r++){
if ((r - l + 1) >= k * 3 && tuura(l , r))
chmin(ans , (r - l + 1) - 3 * k);
}
}
cout << (ans != 1e9 ? ans : -1) << "\n";
}
signed main() {
io();
int t = 1;
//~ cin >> t;
while(t--)
solve();
return 0;
}
