#define mygc(c) (c)=getchar()
static void read1(int *x){int k,m=0;*x=0;for(;;){mygc(k);if(k=='-'){m=1;break;}if('0'<=k&&k<='9'){*x=k-'0';break;}}for(;;){mygc(k);if(k<'0'||k>'9')break;*x=(*x)*10+k-'0';}if(m)(*x)=-(*x);}
static void read2(int *x, int *y){read1(x);read1(y);}

int main(void) {
    int     a,c;

    read2( &a, &c );
	printf("%d\n", a ^ c );
	return 0;
}