Data Validation - Is there a way to surpass the 255 characters limit?

I had created the below formula, which is used for a drop-down list I am preparing. But when I came to paste it in the data validation box, it turned out that I can't insert more than 255 characters, while mine is 776 characters. Any help?

=IF(C2="Humanities List I",IF(C3="English",ENGL1,IF(C3="Others",_OTH1,IF(C2="Humanities List II",IF(C3="American and Media Studies",AMST2,IF(C3="Arabic and Near Eastern Languages",ARAB2,IF(C3="Architecture",ARCH2,IF(C3="Archeology",AROL2,IF(C3="English",ENGL2,IF(C3="Fine Arts and Art History",FAAH2,IF(C3="History",HIST2,IF(C3="Philosophy",PHIL2,IF(C3="Others",_OTH2,IF(C2="Natural Sciences",IF(C3="Others",OTHNS,IF(C2="Quantitative Thoughts",IF(C3="Others",OTHQT,IF(C2="Social Sciences List I",IF(C3="Others",OTHSS1,IF(C2="Social Sciences List II",IF(C3="Economics",ECON2,IF(C3="Education",EDUC2,IF(C3="Political Studies and Public Administration",PSPA2,IF(C3="Sociology and Media Studies",_SMS2,IF(C3="Others",OTHSS2,INDIRECT(SUBSTITUTE(C3," ","")))))))))))))))))))))))))))