No Abstracts.

Now I have abstracts.

Damn it! Useless IBus, now I cannot input Chinese!

# Des.

First we make $f[i]$ as the probability of hit $i$ times among $k$ times in a round. We can also get the probability of getting 1 life point back.
So we get $p[i][j]$ as the probability of changing life points from $i$ to $j$ in one round.
Then we can list the expectation of answers when our target have $i$ points left. That is:
Notice that when one has $n$ points, he cannot get life increased.
As we deal the expression, we would find that all expectations only have to do with $E_1$ and $E_2$, so we can calculate the factor before $E_1$ and $E_2$ for each $i$ in range $[1,n]$.