#include<bits/stdc++.h>
using namespace std;
int kaijo(int x){
    int result=1;
    while(x){
        result *= x;
        x--;
    }
    return result;
}
int narabekata(int m,int n){
    int result;
    result = kaijo(m+n)/(kaijo(m)*kaijo(n));
    return result;
}
int main(){
    int i;
    int N;
    int answer=0;
    scanf("%d", &N);
    for(i=0; i<=N/2; i++){
        answer += narabekata(N-i*2,i);
    }
    printf("%d", answer);
    return 0;
}