import sys
if __name__ == '__main__':
    X,Y = list(map(int,input().split()))
    N = int(input())
    A = list(map(float,input().split()))
    X *= 1000
    Y *= 1000
    TA,TB = [a/X for a in A],[a/Y for a in A]
    for i in range(N-1):
        if(TA[i] > TB[i+1]):
            print("NO")
            sys.exit()
    print("YES")