#include <bits/stdc++.h>
//Soltan Cristian
#define fri(a, b) for (int i = (a); i < (b); ++i)
#define frj(a, b) for(int j = a; j < b; j++)
#define frk(a, b) for(int k = a; k < b; k++)
#define frm(a, b, i) for(int i = b; i >= a; i--)
#define ll long long
#define all(x) x.begin(), x.end()
#define mod 1000000007
#define pb push_back
#define st first
#define nd second
#define sz(x) (ll)x.size()
#define rall(x) x.rbegin(), x.rend()
#define ct(x) cout << x
#define cts(x) cout << x << ' '
#define ctn(x) cout << x << '\n'
#define Y cout << "YES" << '\n'
#define N cout << "NO" << '\n'
using namespace std;
using vi = vector<int>;
using vl = vector<ll>;
using vs = vector<string>;
using vb = vector<bool>;
using ml = map<ll, ll>;
using vii = vector<vector<int>>;
using vll = vector<vector<ll>>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int dx[] = {-1, 0, 1, 0};
const int dy[] = {0, 1, 0, -1};
template <typename T>void read(T n, vector<T> &a){fri(0, n){cin >> a[i];}}
template<typename T>void print(T n, T m, vector<vector<T>> &dp){fri(0, n){ct('\n');frj(0, m){ct(setw(5));cts(dp[i][j]);}}}
const int mxa = 1e9 + 1;
// string __fname = "exclusiv";
// ifstream in(__fname + ".in");
// ofstream out (__fname + ".out");
// #define cin in
// #define cout out
void solve(){
int n, k;
cin >> n >> k;
string s;
cin >> s;
int rs = INT_MAX;
vector<char> q = {'J', 'O', 'I'};
for(int i = 0; i < n - k * 3 + 1; i++){
vector<int> a = {k, k, k};
for(int j = i; j < n; j++){
if(a[0]){
if(s[j] == q[0]){
a[0]--;
}
continue;
}
else if(a[1]){
if(s[j] == q[1]){
a[1]--;
}
continue;
}
else if(a[2]){
if(s[j] == q[2]){
a[2]--;
}
else continue;
}
if(!a[0] && !a[1] && !a[2]){
rs = min(rs, j - i - (k * 3) + 1);
break;
}
}
}
if(rs == INT_MAX){
cout << -1 << '\n';
}
else cout << rs << '\n';
}
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0); ct(fixed); ct(setprecision(10));
// int t;
// cin >> t;
// while(t--)
solve();
return 0;
}
