#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()
const int maxn = 200500;
int n, k;
string s;
int psa[5][maxn];
int query(int i, int l, int r) {
return psa[i][r] - psa[i][l-1];
}
signed main() {
ios::sync_with_stdio(0);
cin.tie(0);
cin >> n >> k;
cin >> s;
s = "."+s;
for(int i = 1; i <= n; i++) {
if(s[i] == 'J') psa[1][i]++;
if(s[i] == 'O') psa[2][i]++;
if(s[i] == 'I') psa[3][i]++;
}
for(int i = 1; i <= 3; i++) {
for(int j = 1; j <= n; j++) {
psa[i][j] += psa[i][j-1];
}
}
int ans = 1e18;
// start j from i
for(int i = 1; i <= n; i++) {
int l = 1, r = n;
int lg = -1;
while(l <= r) {
int mid = (l+r)/2;
if(query(1, i, mid) >= k) {
r = mid-1;
lg = mid;
} else {
l = mid+1;
}
}
if(lg == -1) continue;
int lst = lg;
l = lst+1, r = n;
lg = -1;
while(l <= r) {
int mid = (l+r)/2;
if(query(2, lst+1, mid) >= k) {
r = mid-1;
lg = mid;
} else {
l = mid+1;
}
}
if(lg == -1) continue;
lst = lg;
l = lst+1, r = n;
lg = -1;
while(l <= r) {
int mid = (l+r)/2;
if(query(3, lst+1, mid) >= k) {
r = mid-1;
lg = mid;
} else {
l = mid+1;
}
}
if(lg == -1) continue;
ans = min(ans, lg-i+1 - 3*k);
}
if(ans == 1e18) {
cout << -1 << endl;
} else {
cout << ans << endl;
}
}
/*
find smallest subarray with k-level JOI as subsequence
bsearch
10 2
OJIJOIOIIJ
9 3
JJJOOOIII
9 3
IIIOOOJJJ
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?
*/
