#include <bits/stdc++.h> #define int long long #define pb push_back using namespace std; const int N=1e6+10; const int inf=8e18; const int mod=1e9+7; int s[N]; signed main() { ios_base::sync_with_stdio(NULL); cin.tie(NULL); int T=1; // cin>>T; while(T--) { int n,k; cin>>n>>k; string s; cin>>s; int cnt=0; int pos=0,ans=n-3*k; for(int i=0;i<n;i++) { if(cnt<k) { if(s[i]!='J') continue; if(!cnt) ans-=i-1; cnt++; } else if(cnt<k*2) { if(s[i]!='O') continue; cnt++; } else if(cnt<k*3) { if(s[i]!='I') continue; cnt++; if(cnt==k*3) ans-=n-i; } } if(cnt!=k*3) { cout<<"-1\n"; } else cout<<ans<<"\n"; } }