B (ODS)

#include <bits/stdc++.h>

using namespace std;

const int N = 1e6 + 5;
const int mod = 2020;

int dp[N];

int binpow(int a, int n) {
    if (n == 0) return 1;
    if (n % 2 == 1) {
        int b = binpow(a, n - 1);
        return (b * a) % mod;
    } else {
        int b = binpow(a, n / 2);
        return (b * b) % mod;
    }
}

int main(){
    int n;
    cin >> n;

    dp[1] = 9;

    for (int i = 2; i <= n; i++) {
        dp[i] = (dp[i - 1] * 10 + dp[i - 2] * 9 * 2) % mod;
    }

    int res = dp[n];
    res -= (binpow(10, n - 1) * 9) % mod;
    if (res < 0) res += mod;

    cout << res << endl;
}