import sys, re
from collections import deque, defaultdict, Counter
from math import ceil, sqrt, hypot, factorial, pi, sin, cos, tan, asin, acos, atan, radians, degrees#, log2
from itertools import accumulate, permutations, combinations, combinations_with_replacement, product, groupby
from operator import itemgetter, mul
from copy import deepcopy
from string import ascii_lowercase, ascii_uppercase, digits
from bisect import bisect, bisect_left, insort, insort_left
from fractions import gcd
from heapq import heappush, heappop
from functools import reduce
def input(): return sys.stdin.readline().strip()
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(): return list(map(int, input().split()))
def ZIP(n): return zip(*(MAP() for _ in range(n)))
sys.setrecursionlimit(10 ** 9)
INF = float('inf')
mod = 10**9 + 7
#from decimal import *


N = INT()
S = input()

b = [0]*(N-1)
w = [0]*(N-1)

tmp_b = 0
for i in range(N-1):
	if S[i] == "#":
		tmp_b += 1
	else:
		tmp_b = 0
	b[i] = tmp_b

tmp_w = 0
for i in range(N-1, 0, -1):
	if S[i] == ".":
		tmp_w += 1
	else:
		tmp_w = 0
	w[i-1] = tmp_w

ans = [min(b[i], w[i]) for i in range(N-1)]

#print(b)
#print(w)
#print(ans)
print(sum(ans))

