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

#include<atcoder/modint>
using namespace atcoder;
using mint=modint998244353;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    ll N;
    cin>>N;
    vector<ll> C(4,0);
    for(int i=0;i<N;i++){
        ll A,B;
        cin>>A>>B;
        int c=0;
        while(A%2==0){
            A/=2;
            c++;
        }
        c=min(c,3);
        C[c]+=B;
    }
    ll an=C[3];
    ll d=min(C[1],C[2]);
    an+=d;
    C[1]-=d;
    C[2]-=d;
    an+=(C[1]/3)+(C[2]/2);
    cout<<an<<"\n";
}