#include <bits/stdc++.h>
#define int long long
#define endl '\n'
using namespace std;
const int maxn = 2e5 + 5;
const int inf = 1e18;
int change(char ch){
if (ch == 'J') return 1;
if (ch == 'O') return 2;
if (ch == 'I') return 3;
return 0;
}
int pre[maxn][4], n, k;
string s;
int sech(int l, int r, int type, int val){
int res = 0;
while (l <= r){
int mid = (l + r) >> 1;
if (pre[mid][type] >= val){
res = mid;
r = mid - 1;
} else l = mid + 1;
}
return res;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
cin >> n >> k;
cin >> s;
s = '$' + s;
for (int i = 1; i <= n; i++){
for (int j = 1; j <= 3; j++) pre[i][j] = pre[i - 1][j];
pre[i][change(s[i])]++;
}
int ans = inf;
for (int i = 1; i <= n; i++){
int lastJ = sech(1, n, 1, pre[i - 1][1] + k);
if (!lastJ or lastJ > n) continue;
int lastO = sech(lastJ, n, 2, pre[lastJ - 1][2] + k);
if (!lastO or lastO > n) continue;
int lastI = sech(lastO, n, 3, pre[lastO - 1][3] + k);
if (!lastI or lastI > n) continue;
ans = min(ans, lastI - i + 1 - 3 * k);
}
cout << (ans == inf ? -1 : ans);
return 0;
}
