#include <iostream>
#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,b) for (int i = (a); i <= (b); i++)
#define repa(i,a,b) for (int i = (a); i >= (b); i--)
#define lli long long int
#define debugsl(a) cout << #a << " = " << a << ", "
#define debug(a) cout << #a << " = " << a << endl
#define pos first
#define id second
#define MAX 200000
lli n,k,a,res,J,O,I,o,i;
lli Jid[MAX+2],Oid[MAX+2],Iid[MAX+2],ini[MAX+2];
char arr[200002];
set< pair <lli,lli> > Os, Is;
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cin >> n >> k;
rep(i,1,n) {
cin >> arr[i];
if (arr[i] == 'J') {
J++;
if (J >= k) Jid[J-k+1] = i;
ini[J] = i;
}
else if (arr[i] == 'O') {
O++;
Os.insert({i,O});
if (O >= k) Oid[O-k+1] = i;
}
else if (arr[i] == 'I') {
I++;
Is.insert({i,I});
if (I >= k) Iid[I-k+1] = i;
}
}
res = -1;
rep(j,1,J) {
if (Jid[j] == 0) break;
if (Os.upper_bound({Jid[j],0}) == Os.end()) break;
o = (*Os.upper_bound({Jid[j],0})).id;
if (Oid[o] == 0) break;
if (Is.upper_bound({Oid[o],0}) == Is.end()) break;
i = (*Is.upper_bound({Oid[o],0})).id;
if (Iid[i] == 0) break;
a = (Iid[i]-ini[j]+1)-(k*3);
if (a < res || res == -1) res = a;
}
cout << res;
return 0;
}
