#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/rope>
#define ll long long
#define pb push_back
#define sz(x) (int)(x).size()
#define mp make_pair
#define f first
#define s second
#define all(x) x.begin(), x.end()
#define D(x) cerr << #x << " is " << (x) << "\n";
#define ld long double
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update>; ///find_by_order(),order_of_key()
template<class T1, class T2> ostream& operator<<(ostream& os, const pair<T1,T2>& a) { os << '{' << a.f << ", " << a.s << '}'; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const deque<T>& a){os << '{';for(int i=0;i<sz(a);i++){if(i>0&&i<sz(a))os << ", ";os << a[i];}os<<'}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const set<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T> ostream& operator<<(ostream& os, const multiset<T,greater<T> >& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
template<class T1,class T2> ostream& operator<<(ostream& os, const map<T1,T2>& a) {os << '{';int i=0;for(auto p:a){if(i>0&&i<sz(a))os << ", ";os << p;i++;}os << '}';return os;}
const int N=2e5+5;
int sum[N][3],nxt[N][3];
int getSum(int l,int r,int i){
int ans=sum[r][i];
if(l)
ans-=sum[l-1][i];
return ans;
}
int main()
{
//freopen("in.txt","r",stdin);
//freopen("out.txt","w",stdout);
int n,k;
scanf("%i %i",&n,&k);
string s;
cin >> s;
for(int i=0;i<n;i++){
if(s[i]=='J')
sum[i][0]++;
if(s[i]=='O')
sum[i][1]++;
if(s[i]=='I')
sum[i][2]++;
if(i)
for(int j=0;j<3;j++)
sum[i][j]+=sum[i-1][j];
}
for(int i=0;i<n;i++){
for(int j=0;j<3;j++){
int l=i,r=n-1;
while(l<r){
int m=(l+r)>>1;
int s=getSum(i,m,j);
if(s<k)
l=m+1;
else
r=m;
}
int s=getSum(i,l,j);
if(s!=k)
nxt[i][j]=-1;
else
nxt[i][j]=l;
}
}
int mn=INT_MAX;
for(int i=0;i<n;i++){
int tr=i;
for(int j=0;j<3;j++)
if(tr!=-1)
tr=nxt[tr][j];
if(tr==-1)
continue;
int ostalo=tr-i+1-3*k;
mn=min(mn,ostalo);
}
if(mn==INT_MAX)
mn=-1;
printf("%i\n",mn);
return 0;
}
