#include<bits/stdc++.h>
using namespace std;
#define ll long long
const bool Multitest = 0;
const int N = 2e5 + 10;
int n, k;
int cnt[N][26]; string s;
int get(int p, int x)
{
if(p == -1) return p;
int l = p, r = n, pos = -1;
while(l <= r)
{
int mid = (l + r) >> 1;
// cout << l << ' ' << r << ' ' << mid << '\n';
if(cnt[mid][x] - cnt[p - 1][x] >= k) r = mid - 1, pos = mid;
else l = mid + 1;
}
return pos;
}
void work()
{
cin >> n >> k >> s;
s = '0' + s;
for(int i = 1 ; i <= n ; i++)
{
for(int j = 0 ; j < 26 ; j++) cnt[i][j] += cnt[i - 1][j];
cnt[i][s[i] - 'A']++;
}
vector<int> c;
c.push_back('J' - 'A');
c.push_back('O' - 'A');
c.push_back('I' - 'A');
int ans = 1e9;
// cout << get(2, 'J' - 'A') << '\n';
// return;
for(int i = 1 ; i <= n ; i++)
{
if(s[i] == 'J')
{
int l = i, r = i;
for(int x : c)
{
r = get(r, x);
// cout << x << ' ' << r << '\n';
}
if(r != -1) ans = min(ans, r - l + 1);
}
}
cout << (ans != 1e9 ? ans - 3 * k : -1);
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int q = 1;
if(Multitest) cin >> q;
while(q--) work();
}
