#yuki_512
import sys

x,y=map(int,raw_input().split())
n=int(raw_input())
a=map(int,raw_input().split())
for i in xrange(n-1):
 if 1.0*a[i+1]/y<1.0*a[i]/x:
  print 'NO'
  sys.exit()
print 'YES'