Its showing error while submitting

#include
using namespace std;
int main() {
long long n;
cin>>n;
long long a[n],b[n],k=0;
long long count[1000000]={0};
for(int i=0;i<n;i++){
cin>>a[i];
}
for(int i=0;i<n;i++){
int val=a[i];
count[val]++;

   if(val>k){
       k=val;
   }
}

for(int i=1;i<=k;i++){
    count[i]+=count[i-1];
}
for(int i=n-1;i>=0;i--){
   
    b[--count[a[i]]]=a[i];
}
for(int i=0;i<n;i++){
    a[i]=b[i];
}
for(int i=0;i<n;i++){
    cout<<a[i]<<" ";
}
return 0;

}

Corrected code,

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