#include using namespace std; typedef long long ll; const int MAXN = 55; ll dp[MAXN]; int main() { int N; scanf("%d", &N); memset(dp, 0, sizeof(dp)); dp[0] = 1; for (int i = 0; i <= N; ++i) { dp[i + 1] += dp[i]; dp[i + 2] += dp[i]; } printf("%lld\n", dp[N]); return 0; }