statistics

I have a dataset with age groups as individual variables with counts and I want to create one age group variable with all the options in that variable and combine some age groups as well: HAVE: age_grp_1 = 345 age_grp_2 = 123 age_grp_3 = 46 age_grp_4 = 35 age_grp_5 = 232 age_grp_6 = 372

WANT: age_grp variable with the following values 1= 345 2 = 123 3 = 46 + 35 (combine groups 3&4 above) 4 = 232 5 = 372

Anyone know how to do this? Thanks in advance!