As = 'abcdefghijklmnopqrstuvwxyz'
def solve(N, As):
    if N == 0:
        return ''
    if N == 1:
        return As[0]
    m = int(N**0.5) + 1
    while m * (m+1) > N:
        m -= 1
    n = N - m * (m + 1)
    return As[0:2] * m + solve(n, As[2:])
    
N = int(input())
print(len(solve(N, As)))