#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
template<typename T> using Tree = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
typedef long long int ll;
typedef long double ld;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
#define fastio ios_base::sync_with_stdio(false); cin.tie(NULL)
#define pb push_back
#define endl '\n'
#define sz(a) (int)a.size()
#define setbits(x) __builtin_popcountll(x)
#define ff first
#define ss second
#define conts continue
#define ceil2(x,y) ((x+y-1)/(y))
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define rep(i,n) for(int i = 0; i < n; ++i)
#define rep1(i,n) for(int i = 1; i <= n; ++i)
#define rev(i,s,e) for(int i = s; i >= e; --i)
#define trav(i,a) for(auto &i : a)
template<typename T>
void amin(T &a, T b) {
a = min(a,b);
}
template<typename T>
void amax(T &a, T b) {
a = max(a,b);
}
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) 42
#endif
/*
read the edi some time ago, remember some ideas from there
*/
const int MOD = 1e9 + 7;
const int N = 1e5 + 5;
const int inf1 = int(1e9) + 5;
const ll inf2 = ll(1e18) + 5;
void solve(int test_case)
{
int n,k; cin >> n >> k;
string s; cin >> s;
s = "$" + s;
n <<= 1;
vector<int> p(n+5);
rep1(i,n) p[i] = p[i-1]+(s[i]=='A');
int dp[n+5][n+5][n+5][n+5][n+5];
memset(dp,0x3f,sizeof dp);
dp[0][0][0][0][0] = 0;
rep(i,n){
int x = p[i+1];
rep(ignore_cnt,n+1){
rep(ones,n+1){
rep(active_ones,n+1){
rep(c,n+1){
int curr = dp[i][ignore_cnt][ones][active_ones][c];
// A
amin(dp[i+1][ignore_cnt][ones+1][active_ones+1][c+(active_ones==0)],curr+abs(ones+1-x));
// B
if(ignore_cnt){
amin(dp[i+1][ignore_cnt-1][ones][active_ones][c],curr+abs(ones-x));
}
else{
if(active_ones){
amin(dp[i+1][active_ones-1][ones][0][c],curr+abs(ones-x));
}
}
}
}
}
}
}
int ans = inf1;
rep(c,k+1){
amin(ans,dp[n][0][n/2][0][c]);
}
cout << ans << endl;
}
int main()
{
fastio;
int t = 1;
// cin >> t;
rep1(i, t) {
solve(i);
}
return 0;
}
