h, idx= [0]*100010, 0

def push(x):
    global idx
    h[idx] = x
    idx += 1

def pop():
    global idx
    idx -= 1

def empty():
    global idx
    if idx == 0:
        return 'YES'
    return 'NO'

def query():
    global idx
    return h[idx-1]

def operate(s):
    op = s.split()[0]

    if op == 'push':
        x = s.split()[1]
        push(x)

    elif op == 'pop':
        pop()

    elif op == 'empty':
        print(empty())

    elif op == 'query':
        print( query())



if __name__ == "__main__":
    n = int(input())

    for i in range(n):
        s = input()
        operate(s)