notwithstanding answers to questions asked:
millions portion:
=ROUNDDOWN(MOD(A1,1000000000),-6) or =ROUNDDOWN(MOD(A1,10^9),-6)
thousands:
=ROUNDDOWN(MOD(A1,1000000),-3) or =ROUNDDOWN(MOD(A1,10^6),-3)
hundreds:
=ROUNDDOWN(MOD(A1,1000),0) or =ROUNDDOWN(MOD(A1,10^3),0)
...amongst other approaches