#include<iostream>
using namespace std;
int main(){
    int a=0,b=1;
    int x;
    cin >> x;
    int i=0;
    while(i<x-1){
        int c = a + b;
        a = b;
        b = c;
        i++;
    }
    cout << a << endl;
    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#define Max_N 100
int memo[Max_N+1];
void init_memo(){
    for(int i=0;i<Max_N;i++){
        memo[i]=-1;
    }
}
int fib(n){
    if(n==0) return 0;
    if(n==1||n==2) return 1;
    if(memo[n]!=-1){
        return memo[n];
    }
    memo[n]=fib(n-2)+fib(n-1);
    return memo[n];
}
int main(void){
    int n;
    init_memo();
    scanf("%d",&n);
    if(n<0){
        return -1;
    }
    printf("%d",fib(n-1));
    return 0;
}