≈第一题

#include <iostream>
using namespace std;

long long d = 1, b = 1, c;

void a(int n) {
    if (n == 1) {
        cout << d;
        return ;
    }
    
    c = b;
    b = d + c;
    d = c;
    a(n - 1);
}

int main() {
    long long n;
    cin >> n;
    a(n);
    
    return 0;
}