#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> ii;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<ll> vll;
typedef vector<pll> vpll;
#define PB push_back
#define PF push_front<<
#define PPB pop_back
#define PPF pop_front
#define X first
#define Y second
#define MP make_pair
#define all(x) (x).begin(), (x).end()
const int mod = 1e9 + 7; //998244353;
const int inf = 1e9 + 7;
const ll INF = 1e18 + 7;
const int logo = 20;
const int MAXN = 1e6 + 7;
const int off = 1 << logo;
const int trsz = off << 1;
const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, -1, 1};
vi p[27];
int k;
//kti >= x
int kth(int id, int x){
int it = lower_bound(all(p[id]), x) - p[id].begin() + k - 1;
if(it >= (int)p[id].size()) return inf;
return p[id][it];
}
void solve(){
int n;
cin >> n >> k;
for(int i=1; i<=n; i++){
char x;
cin >> x;
p[x - 'A'].PB(i);
}
int a = 'J' - 'A';
int b = 'O' - 'A';
int c = 'I' - 'A';
int ans = inf;
for(auto &l : p['J' - 'A']){
int pr = kth(a, l);
pr = kth(b, pr);
pr = kth(c, pr);
if(pr < inf) ans = min(ans, pr - l + 1);
}
if(ans == inf) cout << -1 << "\n";
else cout << ans - 3 * k << "\n";
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int tt = 1;
//cin >> tt;
while(tt--) solve();
return 0;
}
