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  1. #include <iostream>
  2. #include <cstdio>
  3. using namespace std;
  4.  
  5. int main() {
  6. 	long long int n, a, cnt;
  7. 	cnt=0;
  8. 	scanf("%lld", &n);
  9. 	for(int i=0; i<n; i++) scanf("%lld", &a), cnt+=a;
  10. 	if(n*(n+1)/2==cnt) printf("YES\n");
  11. 	else printf("NO\n");
  12. 	return 0;
  13. }
Success #stdin #stdout 0s 3344KB
comments ()
stdin
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5
1 1 1 1 1
stdout
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NO
https://ideone.com/HuRk2m
language:
C++ (gcc 8.3)
created:
11 years ago
visibility:
public

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