N = int(input())

X = [0] * 11

for _ in range(N):
    
    for i in map(int, input().split()):
        
        X[i] += 1


x = 0
  
for i in range(11):
    
    x += X[i] // 2
    
    X[i] = X[i] % 2
    

y = sum(X)

print(x + y // 4)