Codeforces Round #563 (Div. 2)C. Ehab and a Special Coloring Problem

 1 #include"iostream"
 2 #include"algorithm"
 3 #include"cstring"
 4 using namespace std;
 5 long long  a[2000006],n;
 6 int main(){
 7     cin>>n;
 8     long long  flag = 1;
 9     memset(a,0,sizeof(a));
10     for(int i=2;i<=n;i++){
11         if(a[i]==0){
12             a[i]=flag;
13             for(int j=i*2;j<=n;j+=i)
14              if(a[j]==0)
15               a[j]=flag;
16               flag++;
17         }
18         cout<<a[i];
19         if(i<n)
20         cout<<" ";
21     }
22     return 0;
23 }