import math

d = int(input())
hl = [int(input()) for i in range(3)]

# 3 3 4 or 3 3 2
if hl[1] == hl[0] or hl[1] == hl[2]:
    # 0 0 2 NG
    print(1 if hl[1] > 0 else -1)
    exit(0)

# 5 7 5 or 2 0 1
if max(hl) == hl[1] or min(hl) == hl[1]:
    print(0)
    exit(0)

maidx = hl.index(max(hl))
miidx = hl.index(min(hl))
if hl[maidx] - hl[1]  > hl[1] - hl[miidx]:
    print(math.ceil((hl[1] - hl[miidx]) / d) + (0 if (hl[1] - hl[miidx])  % d != 0 else 1))
else:
    print(math.ceil((hl[maidx] - hl[1]) / d) + (0 if (hl[maidx] - hl[1])  % d != 0 else 1))