#include "cstdio"
#include <cstdio>

using namespace std;

int main(){
    int n;
    scanf("%d",&n);
    int a=0,b=1;
    for(int i=2;i<=n;i=i+2){
        a=a+b;
        b=a+b;
    }
    if(n%2==0) printf("%d",a);
    else printf("%d",b);
}