#include <iostream>
using namespace std;
#include <string>
#include <algorithm>
#include <map>

int n, f=-1, mnCows;
int x, s, maxR; //maxR is the smallest distance between a infected and non infected
int cows[1000005];


int main()
{
	cin >> n; maxR = 1e9; mnCows = 0;
	for (int i = 0; i < n; i++)
	{
		cin >> x >> s;
		cows[x] = s+1;
	}
	for (int i = 0; i < 1000005; i++)
	{
		if (f!=-1 && cows[i] != cows[f]) {
			if(cows[i]!=0 && cows[f]!=0){
				if (i - f - 1 < maxR) {
					maxR = i - f - 1;
				}
			}
		}
		if (cows[i] == 1 || cows[i] == 2) {
			f = i;
		}
	}
	f = -1;
	for (int i = 0; i < 1000005; i++)
	{
		if(f==-1 && cows[i]==2){
			mnCows++;
		}
		if (f!=-1 && cows[f] == 1 && cows[i] == 2) {
			mnCows++;
		}
		if (f!=-1 && cows[i] == 2 && cows[f] == 2) {
			if (i - f > maxR) {
				mnCows++;
			}
		}
		if (cows[i] == 1 || cows[i] == 2) {
			f = i;
		}
	}
	cout << mnCows << endl;
}