codeforces749A（python）

n = int(raw_input())
result =[] 
times = n/2
if n%2 == 0:
    for i in range(times):
        result.append(2)   
else:
    for i in range(times-1):
        result.append(2)
    result.append(3)
    
print times   
print " ".join(map(str,result))