I used STL inbuilt accumulate() function to get the solution of this problem and it gives me wrong answer but when I used the same logic but removed accummulate() and calculated the sum manually, my solution got passed. What’s wrong with **accumulate()** function?

Click here to go to the problem and here for the link to my solution.

```
#include<bits/stdc++.h>
using namespace std;
int main() {
int t;
cin>>t;
while(t--){
int n;
cin>>n;
unsigned long long a[n],b[n];
for(int i=0;i<n;i++){
cin>>a[i];
b[i] = a[i] - 1;
}
unsigned long long k = accumulate(b,b+n,1);
cout<<k<<endl;
}
return 0;
}
```