#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
#define cerr if(false) cerr
#define watch(x) cerr << (#x) << " is " << (x) << endl;
#define endl '\n'
#define ld long double
#define int long long
#define pii pair<int, int>
#define fi first
#define se second
#define sz(a) (int)(a).size()
#define all(x) (x).begin(), (x).end()
int n, k;
string s;
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k;
cin >> s;
s = "."+s;
int l = 1, r = n;
int mi = 1e18;
while(l <= r) {
int mid = (l+r)/2;
bool ok = false;
cerr << "trying " << mid << endl;
for(int i = 1; i+mid-1 <= n; i++) {
cerr << "from " << i << endl;
queue<char> Q;
for(char chr: string("JOI")) {
for(int j = 0; j < k; j++) {
Q.push(chr);
}
}
for(int j = 0; j < mid; j++) {
if(sz(Q) and s[i+j] == Q.front()) {
cerr << "on " << i+j << endl;
cerr << "popping " << Q.front() << endl;
Q.pop();
}
}
if(Q.empty()) ok = true;
}
watch(ok)
if(ok) {
mi = mid;
r = mid-1;
} else {
l = mid+1;
}
}
// watch(mi)
if(mi == 1e18) {
cout << -1 << endl;
} else {
cout << mi-3*k << endl;
}
}
/*
find smallest subarray with k-level JOI as subsequence
bsearch
Did you read the bounds?
Did you make typos?
Are there edge cases (N=1?)
Are array sizes proper?
Integer overflow?
DS reset properly between test cases?
Is using long longs causing TLE?
Are you using floating points?
*/
