import std.conv, std.functional, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.container, std.math, std.numeric, std.range, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


int N, K;
string S;

int solve() {
  int ret;
  auto a = S.map!(s => (s == '#')).array;
  int l = N, r = -1;
  foreach (i; 0 .. N) {
    if (a[i]) {
      chmin(l, i);
      chmax(r, i);
    }
  }
  assert(l <= r);
  int k = K;
  for (; k < l; ) {
    ++ret;
    ++k;
    a[k] = !a[k];
  }
  for (; k > l; ) {
    ++ret;
    --k;
    a[k] = !a[k];
  }
  debug {
    writeln(ret, " ", k, " ", a);
  }
  int[] xs;
  foreach (i; l + 1 .. r) {
    if (!a[i]) {
      xs ~= i;
    }
  }
  ret += (r - l);
  foreach (j; 0 .. xs.length / 2) {
    ret += 2 * (xs[2 * j + 1] - xs[2 * j]);
  }
  if (xs.length % 2 != 0) {
    ret += 2 * (r - xs[$ - 1]) - 1;
  }
  return ret;
}

void main() {
  try {
    for (; ; ) {
      K = readInt() - 1;
      S = readToken();
      N = cast(int)(S.length);
      int ans = 100 * N;
      foreach (dir; 0 .. 2) {
        chmin(ans, solve());
        K = N - 1 - K;
        S = cast(string)(cast(ubyte[])(S).dup.reverse);
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}