test

#include
#define int ll 
#define maxn 62

using ll = long long;
using namespace std;

signed main(){
	int n;
	cin >> n;
	int dp1[maxn], dp2[maxn], dp[maxn];
	dp1[1] = 1, dp1[2] = 1, dp1[3] = 2;
	dp2[1] = 0, dp2[2] = 1, dp2[3] = 1;
	dp[1] = 1, dp[2] = 2, dp[3] = 3;
	for(int i = 4; i <= n; ++ i)
		dp1[i] = dp[i-1], dp2[i] = dp1[i-2], dp[i] = dp1[i] + dp2[i];
	cout << dp[n];
	return 0;
}