Find the closest value for a certain year in R

I have this type of data:

iso3year    UHC         cata10
AFG 2010    0.3551409   NA
AFG 2011    0.3496452   NA
AFG 2012    0.3468012   NA
AFG 2013    0.3567721   14.631331
AFG 2014    0.3647436   NA
AFG 2015    0.3717983   NA
AFG 2016    0.3855273   4.837534
AFG 2017    0.3948606   NA
AGO 2011    0.3250651   12.379809
AGO 2012    0.3400455   NA
AGO 2013    0.3397722   NA
AGO 2014    0.3385741   NA
AGO 2015    0.3521086   16.902584
AGO 2016    0.3636765   NA
AGO 2017    0.3764945   NA

and I would like to find the closest value to year 2012 and 2017 (+ ou - 2 years, i.e. for 2012 it can be 2010, 2011, 2013 or 2014 data) for cata10 variable. The output should be :

iso3year_UHC    UHC         year_cata   cata10   
AFG 2012        0.3468012   2013        14.631331
AFG 2017        0.3948606   2016        4.837534
AGO 2012        0.3400455   2011        12.379809
AGO 2017        0.3764945   2015        16.902584

I have tried tones of commands since two days but could not manage to find a solution. Could you please advice on the type of commands to try?

Thank you very much,

N.