1 /**************************************************************
 2     Problem: 3907
 3     User: Tunix
 4     Language: Python
 5     Result: Accepted
 6     Time:1184 ms
 7     Memory:79228 kb
 8 ****************************************************************/
 9 
10 def C(n,m):
11     return fact[n]/fact[m]/fact[n-m];
12 f=raw_input().split(" ");
13 n=int(f[0]);
14 m=int(f[1]);
15 tot=max(n,m)*2;
16 fact=[1];
17 for i in range(1,tot+1):
18     fact.append(fact[-1]*i);
19 c=n-m;
20 ans=C(tot-c,tot/2)-C(tot-c,tot/2+1);
21 print ans;