first_d = input()
first_s = first_d.split()

x_int = int(first_s[0])
y_int = int(first_s[0])
z_int = int(first_s[0])
mura_int = x_int - y_int
mura_count= 0

if mura_int > 0:
    mura_count= mura_count+y_int
elif mura_int < 0:
    mura_count= mura_count+x_int
    
if z_int > mura_int:
    mura_count=int(mura_count+(z_int+mura_int)/2)
elif z_int <mura_int:
    mura_count=mura_count+z_int
elif z_int==mura_int:
    mura_count=mura_count+mura_int
    
print(mura_count)