608 B | 608 chars
import sys
from math import sqrt, pi, sin, factorial
inp = lambda : sys.stdin.readline()[:-1].strip()
mii = lambda x = " " : [*map(int,inp().split(x))]
mfi = lambda x = " " : [*map(float,inp().split(x))]
ii = lambda : int(inp())
fi = lambda : float(inp())
p = print
def solve():
t, d, m = mii()
l = sorted([ii() for _ in range(m)] + [d])
if len(l) == 0:
return ("Y" if d >= t else "N")
z = l[0]
for i in range(1, len(l)):
z = max(z, l[i] - l[i - 1])
return ("Y" if z >= t else "N")
if __name__ == "__main__":
tc = 1
for t in range(1, tc+1):
p(solve())