#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
mt19937_64 rng((int)std::chrono::steady_clock::now().time_since_epoch().count());
const int MAXN = 3e5 + 10;
const int MOD = 1e9 + 7;
#define int long long
int rnd(int x, int y) { // random number generator
int u= uniform_int_distribution<int>(x, y)(rng); return u;
}
void solve(int tc) {
int n, k;
cin >> n >> k;
string s;
cin >> s;
int freq[n+1][3];
for(int i=0; i<3; i++) freq[0][i] = 0;
for(int i=0; i<n; i++) s[i] = (s[i] == 'J' ? '0' : (s[i] == 'O' ? '1' : '2'));
for(int i=1; i<=n; i++) {
for(int j=0; j<3; j++) {
freq[i][j] = freq[i-1][j] + (s[i-1] == j + '0');
}
}
int ans = 1e18;
for(int i=1; i<=n; i++) {
bool valid = 1;
int lb = i, rb = n;
while(lb<rb) {
int mid = (lb+rb) >> 1;
if(freq[mid][0] - freq[i-1][0] >= k) rb = mid;
else lb = mid+1;
}
valid &= (freq[lb][0] - freq[i-1][0] == k);
rb = n;
int sto = lb;
lb++;
while(lb<rb) {
int mid = (lb+rb) >> 1;
if(freq[mid][1] - freq[sto][1] >= k) rb = mid;
else lb = mid+1;
}
valid &= (freq[lb][1] - freq[sto][1] == k);
rb = n;
sto = lb;
lb++;
while(lb<rb) {
int mid = (lb+rb) >> 1;
if(freq[mid][2] - freq[sto][2] >= k) rb = mid;
else lb = mid+1;
}
valid &= (freq[lb][2] - freq[sto][2] == k);
if(valid) ans = min(ans, lb-i + 1 - 3*k);
}
cout << (ans == 1e18? -1 : ans);
}
int32_t main(){
ios::sync_with_stdio(0); cin.tie(0);
int t = 1; //cin >> t;
for(int i=1; i<=t; i++) solve(i);
}
