/*
* Author: Nonoze
* Created: Monday 15/12/2025
*/
#include <bits/stdc++.h>
using namespace std;
#ifndef DEBUG
#define dbg(...)
#endif
// #define cout cerr << "OUT: "
#define endl '\n'
#define endlfl '\n' << flush
#define quit(x) return (void)(cout << x << endl)
template<typename T> void read(T& x) { cin >> x; }
template<typename T1, typename T2> void read(pair<T1, T2>& p) { read(p.first), read(p.second); }
template<typename T> void read(vector<T>& v) { for (auto& x : v) read(x); }
template<typename T1, typename T2> void read(T1& x, T2& y) { read(x), read(y); }
template<typename T1, typename T2, typename T3> void read(T1& x, T2& y, T3& z) { read(x), read(y), read(z); }
template<typename T1, typename T2, typename T3, typename T4> void read(T1& x, T2& y, T3& z, T4& zz) { read(x), read(y), read(z), read(zz); }
template<typename T> void print(vector<T>& v) { for (auto& x : v) cout << x << ' '; cout << endl; }
#define sz(x) (int)(x.size())
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define make_unique(v) sort(all(v)), v.erase(unique(all(v)), (v).end())
#define pb push_back
#define mp(a, b) make_pair(a, b)
#define fi first
#define se second
#define cmin(a, b) a = min(a, b)
#define cmax(a, b) a = max(a, b)
#define YES cout << "YES" << endl
#define NO cout << "NO" << endl
#define QYES quit("YES")
#define QNO quit("NO")
#define int long long
#define double long double
const int inf = numeric_limits<int>::max() / 4;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int MOD = 1e9+7, LOG=20;
void solve();
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
int tt=1;
// cin >> tt;
while(tt--) solve();
return 0;
}
int idx(char c) {
if (c=='J') return 0;
if (c=='O') return 1;
return 2;
}
int n, k, m, q;
vector<int> a;
void solve() {
read(n, k);
string s; read(s);
vector<vector<int>> pre(3, vector<int>(n, 0)), pos(3);
for (int i=0; i<n; i++) {
for (int j=0; i && j<3; j++) pre[j][i] = pre[j][i-1];
pre[idx(s[i])][i]++;
pos[idx(s[i])].pb(i);
}
int cnt0=0, cnt1=0, cnt2=0;
for (int i=0; i<n; i++) {
if (s[i]=='J') cnt0++;
if (cnt0>=k && s[i]=='O') cnt1++;
if (cnt1>=k && s[i]=='I') cnt2++;
}
if (cnt2<k) quit(-1);
int ans=sz(s)-3*k;
for (int i=0; i<=cnt0-k; i++) {
int beg0=pos[0][i], end0=pos[0][i+k-1];
auto it1=lower_bound(all(pos[1]), end0+1);
if (it1==pos[1].end() || distance(pos[1].begin(), it1)+k-1>=sz(pos[1])) continue;
int beg1=*(it1), end1=pos[1][distance(pos[1].begin(), it1)+k-1];
auto it2=lower_bound(all(pos[2]), end1+1);
if (it2==pos[2].end() || distance(pos[2].begin(), it2)+k-1>=sz(pos[2])) continue;
int beg2=*(it2), end2=pos[2][distance(pos[2].begin(), it2)+k-1];
int cur=end2-beg0+1;
cmin(ans, cur-3*k);
}
cout << ans << endl;
}
