#include <iostream>
#include <functional>
#include <algorithm>
#include <vector>
#include <numeric>
#include <utility>
#include <cmath>
#define WATCH(x) std::cout << (#x) << ": " << x << '\n';

struct Input
{
	size_t O_count;
	size_t X_count;
};

Input read_input()
{
	size_t kzahozeni;
	std::cin >> kzahozeni;

	std::string input;
	std::cin >> input;

	size_t O = 0;
	size_t X = 0;
	for(auto c: input)
	{
		if(c == 'X')
			X++;
		else
			O++;
	}

	return {O,X};
}
size_t findMoEdge(Input in)
{
	if(std::min(in.X_count, in.O_count) > 20)
	{
		size_t tmp = in.O_count;
		in.O_count = in.X_count;
		in.X_count = tmp;
	}
	return std::floor(std::sqrt(in.O_count));
}

size_t solve(Input in)
{
	if(!in.X_count || !in.O_count)
		return 0;

	size_t Oedge = findMoEdge(in);
	
	size_t Xedge = Oedge + 2;

	size_t O_zbytek = in.O_count - Oedge*Oedge;
	//size_t X_potreba = Oedge*Oedge - Xedge*Xedge;
	size_t X_potreba = Xedge*Xedge - Oedge*Oedge;
	size_t X_zbytek = in.X_count - X_potreba;
//	WATCH(O_zbytek)
//	WATCH(X_zbytek)
	return 1 + O_zbytek + X_zbytek;	
}

int main()
{
	auto in = read_input();
//	WATCH(in.O_count)
//	WATCH(in.X_count)
	std::cout << solve(in) << '\n'; 

	return 0;
}