How do I extract 801011001, 801011002, 801011003, etc from the variable 'parm'. Example dataset is below

Code:
* Example generated by -dataex-. For more info, type help dataex
clear
input byte idnum str4 idstr str41 parm 
1 "mean" "c.a1_k6_score@801011001.sa2_maincode_2016"   
1 "mean" "c.a1_k6_score@801011002.sa2_maincode_2016"  
1 "mean" "c.a1_k6_score@801011003.sa2_maincode_2016"  
1 "mean" "c.a1_k6_score@801011004.sa2_maincode_2016"   
1 "mean" "c.a1_k6_score@801011005.sa2_maincode_2016"  
1 "mean" "c.a1_k6_score@801011006.sa2_maincode_2016"  
1 "mean" "c.a1_k6_score@801011007.sa2_maincode_2016"  
1 "mean" "c.a1_k6_score@801011008.sa2_maincode_2016"  
1 "mean" "c.a1_k6_score@801011009.sa2_maincode_2016"  
1 "mean" "c.a1_k6_score@801011010.sa2_maincode_2016"  
end
Thank you