#include<bits/stdc++.h>
using namespace std;

int main(){
  using ll=long long;
  int n;
  cin>>n;
  vector<ll> cnt(4);
  for (int i=0;i<n;i++){
    int a,b;
    cin>>a>>b;
    int k=0;
    while (a%2==0){
      a/=2;
      k++;
    }
    cnt[min(k,3)]+=b;
  }
  ll c1=cnt[1],c2=cnt[2],c3=cnt[3];
  ll ans=c3;
  ll x=min(c1,c2);
  c1-=x;c2-=x;
  ans+=x;
  if (c1) ans+=c1/3;
  if (c2) ans+=c2/2;
  cout<<ans<<endl;
}