先预处理出每个1000以内的数是否是斐波那契数，然后按照题意模拟即可

#include <bits/stdc++.h>
using namespace std;
int x[1010];
int main() {
    int n, a, b, c;
    cin >> n; a = 1, b = 1;
    while (b <= 1000) {
        x[b] = 1;
        int o = a; a = b, b = o + b;
    }
    for (int i = 1; i <= n; i++) if (x[i]) printf("O"); else printf("o");
    return 0;
}