#exec({'RUBY_THREAD_VM_STACK_SIZE'=>'100000000'},'/usr/bin/ruby', $0) if !ENV['RUBY_THREAD_VM_STACK_SIZE']

require 'prime'

def inpf() a=gets.chomp.split(" ").map(&:to_f)end

def inps() a=gets.chomp.split(" ")end

def copy(a) Marshal.load(Marshal.dump(a)) end

def kaijo(n,r = 10**9+7)(n < 2)? 1 : (2..n).inject{|memo,u|memo=(memo*u)%r} end

def na(n,d=0) Array.new(n,d)end

def na2(n,m,d=0) Array.new(n){Array.new(m,d)}end

def na3(n,m,l,d=0) Array.new(n){Array.new(m){Array.new(l,d)}}end

def inp() a=gets.chomp.split(" ").map(&:to_i)end

def r_up(a, b) (a+b-1)/b end

def sum(a) a.inject(:+) end

def big(a,b) return (a>b)? a:b end

def small(a,b) return (a<b)? a:b end

m = inp[0]
d = []
m.times{d<<inp}
ans = 0
now = [0,0]
d.each do |a|
  f = na(9,nil)
  nowt = [0,0]
  while true
    now[0] += a[0]
    now[1] += 1
    nowt[0]+=1
    nowt[1] = now[1]
    if(now[0] > 9)
      now[0] = now[0]/10 + now[0]%10
      now[1] += 1
      nowt[1] += now[1]
    end
    a[1] -= 1
    if(f[now[0]] != nil)
      bind = nowt[0] - f[now[0]][0]
      k = a[1]/bind
      bi = now[1] -f[now[0]][1]
      now[1] += k*bi
      a[1] -= k*bind
      break
    end

    f[now[0]] = copy(nowt)
    break if a[1] <= 0
  end
  while true
    break if a[1] <= 0
    now[0] += a[0]
    if(now[0] > 9)
      now[0] = now[0]/10 + now[0]%10
      now[1] += 1
    end
    a[1] -= 1
    break if a[1] <= 0
  end
  h = {}
end
p now[1] -1
# make space for editer