#include <stdio.h>
FILE *au,*fin,*fout;

int main()
{
long nr, a,b;
fin=fopen("adunare.in","rt");
fout=fopen("adunare.out","wt");
au=fopen("au.txt","a+");
while (!feof(au))
fscanf(au,"%ld\n",&nr);


fscanf(fin,"%ld %ld\n",&a,&b);
if (nr%2==1) fprintf (fout,"%ld",a+b);
else fprintf(fout,"%ld",a-b);


fprintf(au,"%ld\n",nr/2);
fclose(au);
fclose(fout);
fclose(fin);

return 0;
}