n,m=map(int,input().split())
s=input()
q=[[],[],[]]
i=0
while i<n:
  if s[i]=="-":
    l=i
    r=i
    while s[r]=="-":
      r+=1
    l-=1
    if s[l]==s[r]=="o":
      if (r-l-1)%2:
        q[0]+=[r-l-1]
      else:
        q[1]+=[r-l-1]
    elif s[l]==s[r]=="x":
      q[2]+=[r-l-1]
    else:
      q[1]+=[r-l-1]
    i=r+1
  else:
    i+=1
a=s.count("o")
b=0
q[0].sort()
for l in q[0]:
  if m>=l//2:
    a+=(l//2)*2+1
    m-=l//2
  else:
    a+=m*2
    m-=m
for l in q[1]:
  if m>=l//2:
    a+=(l//2)*2
    m-=l//2
    if l%2:
      b+=1
  else:
    a+=m*2
    m-=m
q[2].sort()
for l in q[2][::-1]:
  if m>0:
    a+=1
    m-=1
    l-=1
    if m>=l//2:
      a+=(l//2)*2
      m-=l//2
      if l%2:
        b+=1
    else:
      a+=m*2
      m-=m
print(a+min(b,m))