#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include<iostream>
#include<cstdint>
#include<cstddef>
#include<vector>
//#include<atcoder/all>
//using namespace atcoder;
using namespace std;
using i32 = int_fast32_t;
using i64 = int_fast64_t;
using usize = size_t;
using u32 = uint_fast32_t;
using u64 = uint_fast64_t;
using i128 = __int128_t;
using u128 = __uint128_t;
using ld = long double;
template<typename T>
using vec = vector<T>;
#define rep(i, n) for (i64 i = 0; i < (i64)(n); ++i)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define len(hoge) (i64)((hoge).size())
using P = pair<i64,i64>;
void solve(){
}
int main(){
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    i64 n;
    cin >> n;
    vec<i64> dp(n + 1);
    dp[0] = 1;
    for(i32 i = 1; i <= n; i++){
        dp[i] += dp[i - 1];
        if(i - 2 >= 0){
            dp[i] += dp[i - 2];
        }
    }
    cout << dp[n] << endl;
}