import math
r,a,b,n = map(int, input().split())
count=0
#function length_sq() for returning square of the side
def length_sq(tuple,list):
    len = (((list[0]-tuple[0])**2) + ((list[1]-tuple[1])**2))
    return len 
#Coordinates of Point A
A=(a/b,a/b)
#C-ordinates of point B
B=((2*n-(a/b)),2*n-(a/b))
#length of AB
AB2 = length_sq(A,B)
AB = math.sqrt(AB2)

for i in range(-r,r+1):
    for j in range(-r,r+1):
        if(abs(i)+abs(j)<=r):
            #length of BC
            BC2 = length_sq(B,(i,j))
            BC = math.sqrt(BC2)
            #length of AC
            AC2 = length_sq(A,(i,j))
            AC = math.sqrt(AC2)
            try:
                alpha = math.acos((AB2+AC2-BC2)/(2*AB*AC))
                alpha= (alpha*180)/math.pi
                alpha= round(alpha,0)
                
                beta =  math.acos((AB2+BC2-AC2)/(2*AB*BC))
                beta= (beta*180)/math.pi
                beta= round(beta,0)
                
                gamma = math.acos((BC2+AC2-AB2)/(2*BC*AC))
                gamma= (gamma*180)/math.pi
                gamma=round(gamma,0)

                if((180>alpha > 90) or (90<beta<180) or (90<gamma<180) ):
                    count=count+1
                except ZeroDivisionError:
                continue
            except ValueError:
                continue
print(count)