#include <iostream>
#include <string>
#include <math.h>
#include <vector>
using namespace std;

int main() {
    string input;
    unsigned long long int N = 0;
    cin >> N >> input;
    unsigned long long int power = sqrt(N);
    unsigned long long int X = 8;
    unsigned long long int O = 1;
    unsigned long long int next = 3;
    vector<pair<unsigned long long int,unsigned long long int>> table;
    pair<unsigned long long int, unsigned long long int> tmp_pair;
    tmp_pair = make_pair(X, O);
    table.push_back(tmp_pair);
    // X a O
    for (unsigned long long int i = 3; i < power; ++i) {
        X += 4;
        O += next;
        next += 2;
        tmp_pair = make_pair(X, O);
        table.push_back(tmp_pair);
    }
    unsigned long long int count_O = 0;
    unsigned long long int count_X = 0;
    for(unsigned  long long int i = 0; i < input.length(); ++i) {
        if(input[i] == 'X') count_X++;
        else count_O++;
    }
    unsigned long long int sum = table.size();
    if( count_X >= table[table.size()-1].first && count_O >= table[table.size()-1].second ){
        for (unsigned long long int i = 0; i < table.size(); ++i) {
            unsigned long long int res_X = count_X - table[i].first;
            unsigned long long int res_O = count_O - table[i].second;
            sum += res_X + res_O;
        }
        cout << sum << endl;
    }
    else cout << 0 << endl;

    return 0;
}