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 = -1;
  foreach (i; 0 .. N) {
    if (a[i]) {
      l = i;
      break;
    }
  }
  assert(l != -1);
  int k = K;
  for (; k < l; ) {
    ++ret;
    ++k;
    a[k] = !a[k];
  }
  for (; k > l; ) {
    ++ret;
    --k;
    a[k] = !a[k];
  }
  int r = -1;
  foreach_reverse (i; 0 .. N) {
    if (a[i]) {
      r = i;
      break;
    }
  }
  if (r != -1) {
    int[] xs;
    if (a[l]) {
      xs ~= l;
    }
    foreach (i; l + 1 .. r) {
      if (!a[i]) {
        xs ~= i;
      }
    }
    debug {
      writefln("l = %s, r = %s, xs = %s", l, r, xs);
    }
    if (xs == [l]) {
      ret += 3;
    } else {
      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;
      }
    }
  }
  debug {
    writeln("solve ", S, " ", K, " = ", ret);
  }
  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) {
  }
}