#include<bits/stdc++.h>
#define ll                  long long
#define dl                 double
#define pb                push_back
#define F                  first
#define S                  second
#define endl              "\n"
#define rep(i,a,b)       for(i=a;i<b;i++)
#define all(v)             v.begin(),v.end()
#define allr(v)            v.rbegin(),v.rend()
#define mod              1000000007
#define CIN(V,s,n)      for(int i=s;i<n;i++){cin >> V[i];}
#define COUT(V,s,n)   {for(int i=s;i<n;i++){cout <<  V[i] << " "  ;} cout << endl;}
#define fast               ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define CLEAR(V);      for(ll i=0;i<V.size();i++) V[i] = 0;
#define N                  1000LL
#define tmod            998244353
using namespace std;

bool sBs(const pair<int,int> &a,const pair<int,int> &b)
{   return (a.second < b.second);   }

ll SUMD(ll n);
ll BS(vector<ll> &PS,ll s,ll e,ll ser);
ll MI(ll a, ll m);
bool P[N+1];
void Sieve(int n=N);
ll Powb(ll b,ll n);

int main()
{
fast;
ll q=1,t;
//cin >> q;
t= q;
while(q--)
{
    ll n,m,k,i,j,l,r,c=0,g,counter=0,u,v,d,e,w,p,x,y,flag=1;
    //n=m=i=j=l=r=a=t=b=c=u=v=w=p=x=y=0;
    cin >>n >> k;
    string s,s1;
    cin >> s;
    s1 = s;

    for(i=0,j=0;i<k and j<n;j++)
    {
        if(s[j]=='L' and (flag==0 or j!=0))
        {
            while(j<n and s[j]=='L') {
                s[j] = 'R';
                j++;
            }
            i++;
        }
        else if(s[j]=='L' and flag==1)
        {
            while(j<n and s[j]=='L') j++;
            flag = 0;
        }
    }
    if(i<k)
    {
        for(j=0;i<k and j<n;j++)
        {
            if(s[j]=='L' and flag==0)
            {
                while(j<n and s[j]=='L') {
                    s[j] = 'R';
                    j++;
                }
                i++;
            }
        }
    }

    ll ans = 0;
    for(i=0;i<n-1;i++)
    {
        if(s[i]=='R')
        {
            if(s[i]=='R' and s[i+1]=='R')
                ans++;
        }
        else
        {
            if(s[i]=='L' and s[i+1]=='L')
                ans++;
        }
    }

    flag = 1;
    for(i=0, j=n-1;i<k and j>=0;j--)
    {
        if(s1[j]=='R' and (flag==0 or j!=n-1) )
        {
            while(j>=0 and s1[j]=='R') {
                s1[j] = 'L';
                j--;
            }
            i++;
        }
        else if(s1[j]=='R' and flag==1)
        {
            while(j>=0 and s1[j]=='R') {
                j--;
            }
            flag = 0;
        }
    }
    if(i<k)
    {
        for(j=n-1;i<k and j>=0;j--)
        {
            if(s1[j]=='R' and flag==0)
            {
                while(j>=0 and s1[j]=='R') {
                    s1[j] = 'L';
                    j--;
                }
                i++;
            }
        }
    }
   ll ans2 = 0;
    for(i=0;i<n-1;i++)
    {
        if(s1[i]=='R')
        {
            if(s1[i]=='R' and s1[i+1]=='R')
            ans2++;
        }
        else
        {
            if(s1[i]=='L' and s1[i+1]=='L')
            ans2++;
        }
    }
    //cout << s << " " << s1 << endl;
    cout << max(ans,ans2) ;//<< " " << ans << " " << ans2;

}
    return 0;
}

//*****************************************************************************************************************************************

ll Powb(ll b,ll n)
{
    if(n==0) return 1LL;
    if(n==1) return b;
    ll temp = Powb(b,n/2);
    if(n%2==0){return (temp*temp)%mod;}
    else{return (b*((temp*temp)%mod))%mod;}
}

ll SUMD(ll n)
{   ll sum=0;
    while(n>0){sum += n%10;n = n/10;}
    return sum;

}
ll BS(vector<ll> &PS,ll s,ll e,ll ser)
{
    if(s>e)
        return s;
    ll mid = (s+e)/2;
    if(PS[mid]==ser)
    {
        return mid;
    }
    else if(PS[mid] > ser)
    {
        return BS(PS,s,mid-1,ser);
    }
    else
        return BS(PS,mid+1,e,ser);
}
ll MI(ll a, ll m)
{
    ll m0 = m;
    ll y = 0, x = 1;
    if (m == 1)
      return 0;
    while (a > 1)
    {
        ll q = a / m;
        ll t = m;
        m = a % m, a = t;
        t = y;
        y = x - q * y;
        x = t;
    }
    if (x < 0)
       x += m0;
    return x;
}

void Sieve(int n)
{
    memset(P,true,sizeof(P));
    P[0] = false;
    P[1]= false;
    for(ll i=2;i*i<=n;i++)
    {
        if(P[i])
        {
            for(ll j=i*i;j<=n;j+=i)
            {
                P[j]=false;
            }
        }
    }

}


Measured memory_bytes: 512