x=int(input())
ten=[0,1,4]
don=[2,3,5,6]
d=0
p=0
for i in range(700):
    if i%7 in ten:
        d+=2
        p+=2
        if p==x:
            print(d)
            break
    elif i%7 in don:
        d+=1
        p-=1
        if p==x:
            print(d)
            break