#include <bits/stdc++.h>

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;
}