#include <iostream>
#include <vector>
#include <string>
#include <algorithm>  // 添加这行
using namespace std;

vector<string> dp(6001);

string addStrings(string num1, string num2) {
    string res;
    int i = num1.size()-1, j = num2.size()-1;
    int carry = 0;
    while(i >= 0 || j >= 0 || carry) {
        int n1 = i >= 0 ? num1[i--]-'0' : 0;
        int n2 = j >= 0 ? num2[j--]-'0' : 0;
        int sum = n1 + n2 + carry;
        res.push_back(sum%10 + '0');
        carry = sum/10;
    }
    reverse(res.begin(), res.end());
    return res;
}

void precompute() {
    dp[0] = "1";
    dp[1] = "1";
    for(int i = 2; i <= 6000; i++) {
        dp[i] = addStrings(dp[i-1], dp[i-2]);
    }
}

int main() {
    precompute();
    int n;
    cin >> n;
    cout << dp[n] << endl;
    return 0;
}