#include<bits/stdc++.h>
#define rep(i,n,m) for(int i = (n); i <(m); i++)
#define rrep(i,n,m) for(int i = (n) - 1; i >=(m); i--)
using namespace std;
using ll = long long;

int main()
{
    int n;
    cin >> n;
    vector<ll> grid(n+3, 0);
    grid[0] = 1;
    rep(i, 0, n)
    {
        grid[i+1] += grid[i];
        grid[i+2] += grid[i];
    }
    cout << grid[n] << endl;
    return 0;
}