a=int(input())
l="a"+"ba"*a
count=0
for (i,x) in enumerate(l):
    for (j,y) in enumerate(l[i+1:]):
        for k in range(0,j-i):
            if l[i+k]==l[j-k]:
                if k==j-1:
                    count+=1
            elif l[i+k]!=l[j-k]:
                break
print(count)