def giai_quyet_dong_gao():
    try:
        n = int(input())
            
        so_tui_5kg = n // 5
        
        while so_tui_5kg >= 0:
            con_lai = n - (so_tui_5kg * 5)
                     
            if con_lai % 3 == 0:
                so_tui_3kg = con_lai // 3
                print(so_tui_5kg + so_tui_3kg)
                return          
            
            so_tui_5kg -= 1
      
        print("-1")
    except EOFError:
        pass

if __name__ == "__main__":
    giai_quyet_dong_gao()