题解

#include <bits/stdc++.h>
using namespace std;
long long dp[51];
int main() {
    int n;
    cin >> n;
    dp[1] = 0;
    dp[2] = 5;
    dp[3] = 9;

    for (int i = 4; i <= n; i++) {
        dp[i]=dp[i-1]*2-1;
    }

    cout << dp[n];

    return 0;
}