#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;
}