#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;

const int N = 5050;
int n;
long long f[N];

int main(){
    scanf("%d",&n);
    
    f[1]=1,f[2]=2;
    if(n==0){
        printf("0\n");
    }
    
    if(n==1||n==2){
        printf("%d\n",f[n]);
        return 0;
    }
    
    for(int i=3;i<=n;i++){
        f[i] = f[i-1] + f[i-2];
    }
    
    printf("%lld\n",f[n]);
    
    return 0;
    
}