[BOJ] 2193. 이친수

#include <iostream>
#include <algorithm>
using namespace std;
long long int dp[91];

int main(){
    int n;
    cin >> n;
    
    dp[1] = 1;
    dp[2] = 1;
    
    for (int i = 3; i <= n; i++)
        dp[i] = dp[i - 2] + dp[i - 1];
    
    cout << dp[n] << endl;
}