Hello to all,today I solve problem A. Greg and Array and I have and misunderstanding: I have two submission,one get accepted and another get wrong answer on test 11.

the difference between this both submission is the line below:

```
for (i=1;i<=n;i++) dp[i]=dp[i]+dp[i-1];
```

if I change `n with m`

I get Accepted,Can someone explain me **why**,I didn't use element on position bigger than `m`

and I didn't exceed the limits of the array `dp`

???

I'm very interesting why this happens,because during the contest this mistake can cost me one problem.