First, let's look at various winning schemes. That is, what is left after you take it, so that the other party can guarantee that you will win.

(The order between lines in the following three cases is not counted, as long as it conforms to this combination. )

1.@

There is only one left, no explanation.

2.@

@

@

At this time, there is only one in each line. Because only one line can be taken at a time, the other side will go first, so it will win.

3.@@

@@

At this time, no matter how the other party takes it, it can be converted into 1, that is, there is only one coin left, just try it.

3. 1:@@……

@ @ ... (The upper and lower figures are the same). At this time, basically, the other party takes a few. As long as there is more than 1 left in his line, you can take the same number as him in another line to ensure that the upper and lower numbers are consistent, and there will always be a situation of 3. If there's another one in his team, or if he takes it all away ... you know.

4.@

@@

@@@

At this time, no matter how the other party takes it, it can always be converted into the first three situations, so it is also established.

4. 1:@

@@@@……

@ @ @ @ @ ... (The second line is greater than or equal to 4, the third line is greater than or equal to 5, and the third line is more than the second line 1)

Basically, the idea is to find a way to reach 2 or 4, that is, the other party takes a few in the second (or third) line and takes the same number in another line, unless there are three (or two) left in the line he takes, and then takes another line until there are two (or three) left, that is, it reaches 4. If there is 1 left in the line he takes, it depends on the situation 2.

If the opponent takes the only one in the first row, then the third row takes 1, reaching 3. 1.

These are all win-win situations. At this time, we find that the case of 4. 1 is formed by directly removing two in the first line. This is the way to win.