  Type II supernovae represent the most common stellar explosions in the
Universe, for which the final stage evolution of their hydrogen-rich massive
progenitors towards core-collapse explosion are elusive. The recent explosion
of SN 2023ixf in a very nearby galaxy, Messier 101, provides a rare opportunity
to explore this longstanding issue. With the timely high-cadence flash spectra
taken within 1-5 days after the explosion, we can put stringent constraints on
the properties of the surrounding circumstellar material around this supernova.
Based on the rapid fading of the narrow emission lines and luminosity/profile
of $\rm H\alpha$ emission at very early times, we estimate that the progenitor
of SN 2023ixf lost material at a mass-loss rate $\dot{\rm M} \approx 6 \times
10^{-4}\, \rm M_{\odot}\,a^{-1}$ over the last 2-3 years before explosion. This
close-by material, moving at a velocity $v_{\rm w} \approx 55\rm \,
km\,s^{-1}$, accumulates a compact CSM shell at the radius smaller than $7
\times 10^{14}$ cm from the progenitor. Given the high mass-loss rate and
relatively large wind velocity presented here, together with the pre-explosion
observations made about two decades ago, the progenitor of SN 2023ixf could be
a short-lived yellow hypergiant that evolved from a red supergiant shortly
before the explosion.
