输入一个整数a，输出由a构成m行n列的矩阵。请编程实现

a = int(input("请输入整数a："))
m = int(input("请输入行数m："))
n = int(input("请输入列数n："))

for i in range(m):
for j in range(n):
print(a, end=" ")
print()