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  1. #include<bits/stdc++.h>
  2.  
  3. using namespace std;
  4.  
  5. int main(){
  6.     ios::sync_with_stdio(false);
  7. 	cin.tie(0);
  8. //	freopen("in.txt","r",stdin);
  9. 	int n,r,t,cnt=0;
  10. 	cin>>n>>r;
  11. 	for (int i = 0; i <= n; cin>>t, ++i)
  12. 		if(t)
  13. 			cnt++;
  14.  
  15. 	if(!cnt){cout<<"-1"<<endl;return 0;}
  16.  
  17. 	t = ceil((double)n/(2*r-2)); 
  18. 	t = (n>0)?t:1;
  19.  
  20. 	t = (t<=cnt)?t:-1;
  21. 	cout<<(t)<<endl;
  22.  
  23.  
  24. return 0;
  25. }
  26.  
  27.  
  28.  
Success #stdin #stdout 0s 15232KB
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stdin
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5 10

0 0 0 0 0
stdout
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-1
https://ideone.com/XdpmQJ
language:
C++ 4.3.2 (gcc-4.3.2)
created:
5 years ago
visibility:
secret

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