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

string FMT_F = "%.10f";

static string[] s_rd;
T RD(T = long)() { while(!s_rd.length) s_rd = readln.chomp.split; string res = s_rd[0]; s_rd.popFront; return res.to!T; }
string RDR()() { return readln.chomp; }
T[] ARR(T = long)(in string str, T fix = 0) { auto r = str.split.to!(T[]); r[] += fix; return r; }
size_t[] MAKE_IDX(alias less = "a < b", Range)(Range range) { auto idx = new size_t[](range.length); makeIndex!(less)(range, idx); return idx;}
size_t MIN_POS(alias less = "a < b", Range)(Range range) { auto r = minPos!(less)(range); return range.length - r.length; }

bool inside(T)(T x, T b, T e) { return x >= b && x < e; }
bool minimize(T)(ref T x, T y) { if (x > y) { x = y; return true; } else { return false; } }
bool maximize(T)(ref T x, T y) { if (x < y) { x = y; return true; } else { return false; } }

long mod = 10^^9 + 7;
void moda(ref long x, long y) { x = (x + y) % mod; }
void mods(ref long x, long y) { x = ((x + mod) - (y % mod)) % mod; }
void modm(ref long x, long y) { x = (x * y) % mod; }

void main()
{	
	auto N = RD;
	auto S = RD!string;
	/*long N = 2*(10^^5);
	auto SS = new char[][](1);
	foreach (i; 0..1)
	{
		SS[i] = new char[](N);
		foreach (j; 0..N)
			SS[i][j] = dice(0.5, 0.5) == 0 ? '.' : '#';
	}
	
	foreach (S; SS)
	{ writeln(S);*/

	long[] cnt = [0];
	char last = S[0];
	foreach (i; 0..N)
	{
		if (S[i] == last)
		{
			++cnt[$-1];
		}
		else
		{
			cnt ~= 1;
			last = S[i];
		}
	}
	debug writeln(cnt);

	auto b_pos = S[0] == '#' ? 0 : 1;
	auto b = new long[](cnt.length+100);
	auto w = new long[](cnt.length+100);
	foreach (i, e; cnt)
	{
		b[i+1] = b[i];
		
		if (i % 2 == b_pos)
			b[i+1] += e;
	}
	foreach_reverse (i, e; cnt)
	{
		w[i] = w[i+1];
		if (i % 2 != b_pos)
			w[i] += e;
	}

	long ans = long.max;
	foreach (i; 0..cnt.length+1)
	{
		ans = min(ans, w[i] + b[i]);
	}

	writeln(ans);
	stdout.flush();
	//}
	debug readln();
}