import sys
input=lambda: sys.stdin.readline().rstrip()
x,y=map(int,input().split())
n=int(input())
A=[int(i) for i in input().split()]
tx,ty=0,A[0]/y
for i in range(n-1):
  tx+=A[i]/x
  ty+=A[i+1]/y
  if ty<tx:
    print("NO")
    break
else:
  print("YES")