import subprocess as SP
import os
from datetime import timedelta
from datetime import datetime

dt = timedelta(days=1)
d = datetime.today().date()

while True:
    toolchain="nightly-{}".format(d.isoformat())
    ret = os.system(
        f"rustup default {toolchain}"
    )
    if ret==0:
        os.system("cargo +{} clean".format(toolchain))
        if os.system("cargo +{} check".format(toolchain))==0:
            print(d)
            break
    d = d - dt