package backjoon;

// https://www.acmicpc.net/problem/10870

// 피보나치 수 5

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;

public class _10870 {

public static void main(String[] args) throws IOException {

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

// memory 11468 runtime 84

int n = Integer.parseInt(br.readLine());

int first = 0;

int second = 1;

int fibonacci = first + second;

if(n==0){

System.out.println(0);

}

if(n==1){

System.out.println(1);

}

if(n>1){

for(int i=1; i<n; i++){

fibonacci = first + second;

first = second;

second = fibonacci;

}

System.out.println(fibonacci);

}

}

}

/*

input

10

output

55

*/