#include<bits/stdc++.h>
using namespace std; 
int main() { 
    int n; 
    cin >> n; 
    int prev1 = 1;
    int prev2 = 1;
    int current = 1; 
    if (n == 1 || n == 2) { 
        cout << 1 << endl; 
        return 0; 
    }
    for (int i = 3; i <= n; i++) { 
        current = prev1 + prev2;
        prev1 = prev2; 
        prev2 = current; 
    } 
    cout << current << endl; 
    return 0; 
}
/**************************************************************
	Problem: 1238
	User: HUANGYIBO
	Language: C++
	Result: Accepted
	Time:9 ms
	Memory:2072 kb
****************************************************************/