I was trying to solve 732D and after struggling with an optimal algorithm for sometime, I looked into the accepted solutions and saw that many ACs were as simple as the following.

http://mirror.codeforces.com/contest/732/submission/21571861

#include<bits/stdc++.h>  
using namespace std;  
int main()  
{  
int n,m;  
cin>>n>>m;  
int arr[n+1];  
for(int i=1;i<=n;i++)cin>>arr[i];  
int sum=m,x;  
for(int i=0;i<m;i++){cin>>x; sum+=x;}  
  
for(int i=sum;i<=n;i++)if(arr[i]){cout<<i; return 0;}  
cout<<-1;  
}  

I think they will fail on a simple testcase as —

8 2
1 1 1 1 1 1 1 2
1 1

( The ans should be 8 )

Am I understanding the question incorrectly ?

UPDATE It seems like after the contest, some test cases might have been updated/added covering the case above.