You are using pic1 for all:
Change as below
string filename1 = Path.GetFileName(pic1.PostedFile.FileName);
pic1.SaveAs(Server.MapPath("imgs/" + filename1 + ".jpg"));
string filename2 = Path.GetFileName(pic2.PostedFile.FileName);
pic2.SaveAs(Server.MapPath("imgs/" + filename2 + ".jpg"));
string filename3 = Path.GetFileName(pic3.PostedFile.FileName);
pic3.SaveAs(Server.MapPath("imgs/" + filename3 + ".jpg"));
string filename4 = Path.GetFileName(pic4.PostedFile.FileName);
pic4.SaveAs(Server.MapPath("imgs/" + filename4 + ".jpg"));
string filename5 = Path.GetFileName(pic5.PostedFile.FileName);
pic5.SaveAs(Server.MapPath("imgs/" + filename5 + ".jpg"));