firstinput = input();
firsts = firstinput.split(" ");

Adata = int(firsts[0]);
Bdata = int(firsts[1]);

result = 0;
hikakudata=0;

for idata in range(Adata,Bdata+1):
	hikakudata = Adata + Bdata + int(idata);
	if hikakudata %3 == 0:
		result = result + 1;

print(result);