#include <iostream>
#include <vector>
using namespace std;
vector<int> memo;
int f(int n) {
    if (n <= 1) return n;
    if (memo[n] != -1) return memo[n];
    memo[n] = f(n-1) + f(n-2);
    return memo[n];
}
int main() {
    memo.resize(6, -1);
    cout << f(5) << endl;
    return 0;
}