#include<bits/stdc++.h>
using namespace std;
#define DEBUG 0
#define printf if(DEBUG) printf
constexpr int MAXN = 2e5+10;
int to_int(char c) {
//j,o,i
if (c=='J')return 0;
if (c=='O')return 1;
if (c=='I') return 2;
assert(false);
}
vector<vector<int>> pref(3, vector<int>(MAXN)), suff(3, vector<int>(MAXN)); // 0
vector<int> total_count(3,0);
int main() {
int n,k;cin>>n>>k;
string s;cin>>s;
for (int i = 1; i <= n; i++) {
int ch = to_int(s[i-1]);
total_count[ch]++;
for (int c = 0; c < 3; c++) {
pref[c][i] = pref[c][i-1];
if (ch == c) pref[c][i]++;
}
}
for (int i = n; i >= 1; i--) {
int ch = to_int(s[i-1]);
for (int c = 0; c < 3; c++) {
suff[c][i] = suff[c][i+1];
if (ch == c) suff[c][i]++;
}
}
int ans = 1e9;
auto find_next = [&](int i, int c) {
int pref_begin = pref[c][i-1];
// look for first i that is at least pref_begin + k
int l = i, r = n;
int best = -1;
while (l <= r) {
int mid = l+(r-l)/2;
bool ok = (pref[c][mid] >= pref_begin + k);
if (ok) {
best = mid;
r = mid-1;
} else {
l = mid+1;
}
}
return best;
};
for (int idx_start = 1; idx_start <= n; idx_start++) {
printf("idx_start %d\n", idx_start);
int ch = to_int(s[idx_start-1]);
if (ch != 0) continue;
int idx_j = find_next(idx_start, 0);
printf("idx_j %d\n", idx_j);
if (idx_j == -1) continue;
int idx_o = find_next(idx_j+1, 1);
printf("idx_o %d\n", idx_o);
if (idx_o == -1) continue;
int idx_i = find_next(idx_o+1, 2);
printf("idx_i %d\n", idx_i);
if (idx_i == -1) continue;
int this_ans = (idx_i - idx_start+1) - 3 * k;
ans = min(ans, this_ans);
}
if (ans==1e9)ans=-1;
cout<<ans<<endl;
}
