from qiskit.providers.ibmq import least_busy
backend_lb = least_busy(provider.backends(
    filters=lambda x: x.configuration().n_qubits >= 5 and not 
    x.configuration().simulator and 
    x.status().operational==True))
print("Least busy backend: ", backend_lb)

from qiskit import execute
# 最も空いている実機を使用
backend = backend_lb