#include <bits/stdc++.h>
#define pii pair<int, int>
using namespace std;
int N, K;
int sumJ[200005];
int sumO[200005];
int sumI[200005];
int cntJ, cntO, cntI;
void calc(int l, int r) {
cntJ = sumJ[r] - sumJ[l - 1];
cntO = sumO[r] - sumO[l - 1];
cntI = sumI[r] - sumI[l - 1];
}
int main() {
ios_base::sync_with_stdio(0);
cin >> N >> K;
char ch;
for(int i = 1; i <= N; i++) {
cin >> ch;
if(ch == 'J') {
sumJ[i] = 1;
}else if(ch == 'O') {
sumO[i] = 1;
}else {
sumI[i] = 1;
}
sumJ[i] += sumJ[i - 1];
sumO[i] += sumO[i - 1];
sumI[i] += sumI[i - 1];
}
int ans = 1e9;
for(int i = 1; i <= N; i++) {
int l = i, r = N, res = -1;
// cout << i << "\n";
//binser J
while(l <= r) {
int mid = (l + r) >> 1;
calc(i, mid);
if(cntJ >= K) {
res = mid;
r = mid - 1;
}else {
l = mid + 1;
}
}
// cout << res << " J\n";
if(res == -1) break;
//binser O
int bef = res + 1;
l = res + 1, r = N, res = -1;
while(l <= r) {
int mid = (l + r) >> 1;
calc(bef, mid);
if(cntO >= K) {
res = mid;
r = mid - 1;
}else {
l = mid + 1;
}
}
// cout << res << " O\n";
if(res == -1) break;
//binser I
bef = res + 1;
l = res + 1, r = N, res = -1;
while(l <= r) {
int mid = (l + r) >> 1;
calc(bef, mid);
if(cntI >= K) {
res = mid;
r = mid - 1;
}else {
l = mid + 1;
}
}
// cout << res << " I\n";
if(res == -1) break;
ans = min(ans, res - i + 1 - K * 3);
}
if(ans != 1e9) cout << ans << "\n";
else cout << "-1\n";
cin >> N;
}
