import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
sys.setrecursionlimit(10 ** 7)

l, r, m, k = map(int, read().split())
if k == 0:
    k = float('inf')
print('Yes' if k >= m // (r - l) else 'No')