#include<bits/stdc++.h>
using namespace std;
const int MAXN = 2e5 + 5;
#define int long long
int n, k;
string s;
int pre[MAXN][3];
int ans = INT_MAX;
int findd(int t, int pos)
{
int l = pos;
int r = n;
int ans = -1;
while(l <= r)
{
int m = (l + r) / 2;
if (pre[m][t] - pre[pos - 1][t] >= k)
{
ans = m;
r = m - 1;
}
else
{
l = m + 1;
}
}
return ans;
}
signed main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin >> n >> k;
cin >> s;
s = "%" + s;
for (int i = 1; i <= n; i++)
{
for (int j = 0; j <= 2; j++)
{
pre[i][j] = pre[i - 1][j];
}
if (s[i] == 'J')
{
pre[i][0]++;
}
else if (s[i] == 'O')
{
pre[i][1]++;
}
else if (s[i] == 'I')
{
pre[i][2]++;
}
}
for (int i = 1; i <= n; i++)
{
int l = i;
int cur = i;
int nxt = findd(0, cur);
if (nxt == -1)
{
continue;
}
cur = nxt + 1;
nxt = findd(1, cur);
if (nxt == -1)
{
continue;
}
cur = nxt + 1;
nxt = findd(2, cur);
if (nxt == -1)
{
continue;
}
int r = nxt;
ans = min(ans, r - l + 1 - 3 * k);
}
if (ans == INT_MAX)
{
cout << -1;
}
else
{
cout << ans;
}
}
