#include <iostream>
#include <iomanip>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <cfloat>
#include <climits>
#include <ctime>
#include <cassert>
#include <numeric>
#include <functional>
using namespace std;

#define rep(i,a,n) for(int (i)=(a); (i)<(n); (i)++)
#define repq(i,a,n) for(int (i)=(a); (i)<=(n); (i)++)
#define repr(i,a,n) for(int (i)=(a); (i)>=(n); (i)--)
#define int long long int

template<typename T> void chmax(T &a, T b) {a = max(a, b);}
template<typename T> void chmin(T &a, T b) {a = min(a, b);}
template<typename T> void chadd(T &a, T b) {a = a + b;}

typedef pair<int, int> pii;
typedef long long ll;

int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
constexpr ll INF = 1001001001001001LL;
constexpr ll MOD = 1000000007LL;

int N;
int const SIZE = 20;
map<vector<int>, bool> m;

void showvector(vector<int> &v) {
    printf("vector: ");
    rep(i,0,SIZE) {
        printf("%lld ", v[i]);
    }
    cout << endl;
}

bool experiment(vector<int> v) {
    if(m.count(v)) return m[v];
    // showvector(v);
    rep(i,0,SIZE) {
        if(v[i] == 0) continue;
        repq(j,1,v[i]) {
            vector<int> temp = v;
            temp[i] -= j;
            if(!experiment(temp)) {
                m[v] = true;
                return m[v];
            }
            temp[i] += j;
        }
    }
    return m[v] = false;
}

signed main() {
    cin >> N;
    int k = 1;
    while(1) {
        int val = (k+2) * (k+3) / 2 - 3;
        // printf("k = %lld, val = %lld\n", k, val);
        if(val == N) {
            cout << "X" << endl;
            return 0;
        }
        if(val > N) break;
        k++;
    }
    cout << "O" << endl;
    return 0;
}