5 people have 20 unique impressions

5 people have 20 unique impressions:
Amy, Eva, Joy, Kim, Pam:
1. Amy + Eva (Amy of Eva, Eva of Amy) = 2.
2. Amy + Joy = 2.
3. Amy + Kim = 2.
4. Amy + Pam = 2.
5. Eva + Joy = 2.
6. Eva + Kim = 2.
7. Eva + Pam = 2.
8. Joy + Kim = 2.
9. Joy + Pam = 2.
10. Kim + Pam = 2.
Total = 20