Baekjoon #10870

#include <bits/stdc++.h>

using namespace std;

int DP[25];

int main(){
    ios::sync_with_stdio(false); 
    cin.tie(0);

    DP[0] = 0; 
    DP[1] = 1;
    for(int i=2;i<=20;i++){
        DP[i] = DP[i - 1] + DP[i - 2];
    }

    int N; cin >> N;
    cout << DP[N];
}