import sys
input = sys.stdin.readline

N=int(input())
S=input().strip()

A=[]
for i in range(len(S)):
    if S[i]=="#":
        A.append(i)

ANS=-1
ind=0

LA=-1

for i in range(N):
    while ind<len(A) and A[ind]<=i:
        #print(A[ind],i)
        ind+=1

    if ind-1>=0:
        k=A[ind-1]
    else:
        k=-1<<63

    if ind<len(A):
        l=A[ind]
    else:
        l=1<<63

    score=min(i-k,l-i)

    if score>ANS:
        ANS=score
        LA=i

print(LA+1)