import java.math.BigInteger;

public class Euler121 {
    public static void main(String[] args) {
        int turns = 15;
        BigInteger[] dp = new BigInteger[turns + 1];
        for (int i = 0; i <= turns; i++)
            dp[i] = BigInteger.ZERO;
        dp[0] = BigInteger.ONE;
        for (int t = 1; t <= turns; t++) {
            BigInteger[] next = new BigInteger[turns + 1];
            for (int i = 0; i <= turns; i++)
                next[i] = BigInteger.ZERO;
            for (int b = 0; b <= t; b++) {
                if (dp[b].signum() == 0)
                    continue;
                // red: multiply by t (red discs)
                next[b] = next[b].add(dp[b].multiply(BigInteger.valueOf(t)));
                // blue: multiply by 1
                if (b + 1 <= turns)
                    next[b + 1] = next[b + 1].add(dp[b]);
            }
            dp = next;
        }
        BigInteger denom = BigInteger.ONE;
        for (int t = 1; t <= turns; t++)
            denom = denom.multiply(BigInteger.valueOf(t + 1));
        BigInteger winNum = BigInteger.ZERO;
        for (int b = turns / 2 + 1; b <= turns; b++)
            winNum = winNum.add(dp[b]);
        System.out.println(denom.divide(winNum));
    }
}