they asked about a problem in math , so .. here it is
hint : the step in general should be 45 => 60 cm not more
aprox : the human being MAY walk in his entire life the same measure he goes arround the world twice !
P = perimeter of the planet = 2 * 3.14159 * 6400 000 ( 6400 KM = mid_radius of the earth )
so he may walks about 2xP in about 60 years .