from math import sqrt, floor

epsilon = 1e-5

def pyramide(n):
    nb_etages = sqrt(n) - 1
    if abs(floor(nb_etages) - nb_etages) < epsilon:
        return int(2*nb_etages + 1)
    else:
        return -1

if __name__ == '__main__':
    n = int(raw_input())
    print pyramide(n)