#include "bits/stdc++.h"

using namespace std;


int x[1005],y[1005];

bool done[1005];

int main(){
    int n;cin>>n;
    for(int i=0;i<n;i++){
        cin>>x[i]>>y[i];
    }

    //biggest R we can have
    int bigR=1e9;
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            if(y[i]+y[j]==1){//1 infected, 1 not
                bigR=min(bigR,abs(x[i]-x[j])-1);
            }
        }
    }

    vector<pair<int,int>> v;
    for(int i=0;i<n;i++){
        v.push_back({x[i],y[i]});
    }
    sort(v.begin(),v.end());

    int cnt=0;
    for(int i=0;i<n;i++){
        if(v[i].second==1){
            if(i==0){
                cnt++;
            }  else {
                if(v[i-1].second==0){
                    cnt++;
                } else {
                    if(v[i-1].second==1 && v[i].first-v[i-1].first>bigR){
                        cnt++;
                    }
                }
            }
        }
    }
    cout<<cnt<<endl;
}