package adv2017; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.InputMismatchException; public class N608_2 { InputStream is; PrintWriter out; String INPUT = ""; void solve() { int x = ni()-1; char[] s = ns().toCharArray(); long ret = Math.min(go1(s, x), go2(s, x)); if(ret == Long.MAX_VALUE)ret = 3; out.println(ret); } long go1(char[] s, int x) { int n = s.length; int p = 0, q = n-1; int[] f = new int[n]; while(p < n && (s[p] == '#') == (f[p] == 1))p++; if(p >= x)return Long.MAX_VALUE; long ret = x - p; for(int i = p;i < x;i++){ f[i] ^= 1; } while(q >= 0 && (s[q] == '#') == (f[q] == 1))q--; if(p > q)return ret; for(int i = p+1;i <= q;i++){ f[i] ^= 1; ret++; if((f[i] == 1) == (s[i] == '#')){ continue; } if(i+1 == q){ ret += 2; break; } f[i] ^= 1; f[i+1] ^= 1; ret += 2; } return ret; } long go2(char[] s, int x) { int n = s.length; int p = 0, q = n-1; int[] f = new int[n]; while(q >= 0 && (s[q] == '#') == (f[q] == 1))q--; if(q <= x)return Long.MAX_VALUE; long ret = q - x; for(int i = x+1;i <= q;i++){ f[i] ^= 1; } while(p < n && (s[p] == '#') == (f[p] == 1))p++; if(p > q)return ret; for(int i = q-1;i >= p;i--){ f[i] ^= 1; ret++; if((f[i] == 1) == (s[i] == '#')){ continue; } if(i-1 == p){ ret += 2; break; } ret += 2; f[i] ^= 1; f[i-1] ^= 1; } return ret; } public static int sumFenwick(int[] ft, int i) { int sum = 0; for(i++;i > 0;i -= i&-i)sum ^= ft[i]; return sum; } public static void addFenwick(int[] ft, int i, int v) { if(v == 0 || i < 0)return; int n = ft.length; for(i++;i < n;i += i&-i)ft[i] ^= v; } public static int[] restoreFenwick(int[] ft) { int n = ft.length-1; int[] ret = new int[n]; for(int i = 0;i < n;i++)ret[i] = sumFenwick(ft, i); for(int i = n-1;i >= 1;i--)ret[i] ^= ret[i-1]; return ret; } void run() throws Exception { is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); long s = System.currentTimeMillis(); solve(); out.flush(); if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); // Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){ // @Override // public void run() { // long s = System.currentTimeMillis(); // solve(); // out.flush(); // if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); // } // }; // t.start(); // t.join(); } public static void main(String[] args) throws Exception { new N608_2().run(); } private byte[] inbuf = new byte[1024]; public int lenbuf = 0, ptrbuf = 0; private int readByte() { if(lenbuf == -1)throw new InputMismatchException(); if(ptrbuf >= lenbuf){ ptrbuf = 0; try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); } if(lenbuf <= 0)return -1; } return inbuf[ptrbuf++]; } private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; } private double nd() { return Double.parseDouble(ns()); } private char nc() { return (char)skip(); } private String ns() { int b = skip(); StringBuilder sb = new StringBuilder(); while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ') sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } private char[] ns(int n) { char[] buf = new char[n]; int b = skip(), p = 0; while(p < n && !(isSpaceChar(b))){ buf[p++] = (char)b; b = readByte(); } return n == p ? buf : Arrays.copyOf(buf, p); } private int[] na(int n) { int[] a = new int[n]; for(int i = 0;i < n;i++)a[i] = ni(); return a; } private long[] nal(int n) { long[] a = new long[n]; for(int i = 0;i < n;i++)a[i] = nl(); return a; } private char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } private int[][] nmi(int n, int m) { int[][] map = new int[n][]; for(int i = 0;i < n;i++)map[i] = na(m); return map; } private int ni() { return (int)nl(); } private long nl() { long num = 0; int b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); } }