蘑菇街——方格走法

#encoding=utf-8

import sys

x,y=map( lambda x:int( x ),sys.stdin.readline().strip("\n").split(" ") )

res=[[1] * (y + 1) for _ in range(x + 1)]

for i in range(1, x + 1):
    for j in range(1, y + 1):
        res[i][j] = res[i - 1][j] + res[i][j - 1]

print(res[x][y])