the solution is n-th fibonaci number
write every option for evidence


#include <bits/stdc++.h>
using namespace std;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n;
    cin >> n;
    //the answer is F[n] - fibonnaci number
    //76 > 3
    vector <long long> dp(n + 2);
    dp[1] = 2;
    dp[2] = 2;
    for(int i = 3; i <= n; i++)dp[i] = dp[i - 1] + dp[i - 2];
    cout << dp[n];
}