concatenating data sets

data thrdcls ;
input name$ age sex grade$;
datalines;
ali 21 0 2.78
hasan 22 0 3.21
yasemin 21 1 3.52
run;
data thrdcls (rename=(tmp=grade) drop=grade);
set thrdcls;
tmp=input(grade,5.2);
run;
data frthcls;
input name$ age sex grade;
datalines;
mustafa 21 0 3.15
fatam 22 1 2.95
emre 21 0 2.25
selin 22 1 2.70
run;
data std;
set thrdcls frthcls;
run;
proc print; run;