题解 | #统计每个月兔子的总数#

#include <iostream>
using namespace std;

int main() {
    int n, n_0, n_1, n_2, sum;
    cin >> n;
    n_0 = 0;
    n_1 = 0;
    n_2 = 1;
    for (int i = 3; i <= n; ++i){
        n_2 = n_2 + n_1;
        n_1 = n_0;
        n_0 = n_2;
    }
    sum = n_0 + n_1 + n_2;
    cout << sum << endl;
    return 0;
}