P,K,L=map(int,input().split())
Q=list(input())
l=[(L,0)]*K
for i in range(K):
     for j in range(len(Q)-L):
          if Q[j:j+L].count('#')<l[i][0]:
              l[i]=Q[j:j+L].count('#'),j
     del Q[l[i][1]:l[i][1]+L]
print(sum([x[0]for x in l]))