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

int n, f = 0, mnCows;
int x,s,r;
// int size = 1000005;
int cows[1000005];

int main(){

    cin >> n; r = INT_MAX; mnCows=0;
    for(int i = 0; i<n; i++){
        cin >> x >> s;
        cows[x] = s+1;
    }
    for(int i = 0; i<1000005; i++){
        if((cows[i] != cows[f]) && cows[i]!=0 && cows[f] != 0) r = min(r,i-f-1);
        if(cows[i] == 1 || cows[i] == 2) f = i;
    }
    f = 0;


    for(int i = 0; i<1000005; i++){

        if(cows[f] == 1 && cows[i] == 2) {
            mnCows++;
        }
        if(cows[i] == 2 && cows[f] == 2){
            if(i-f > r){
                mnCows++;
            }
        }
        if(cows[i] == 1 || cows[i] == 2){
            f=i;
        }
    }

    for(int i = 0; i<1000005; i++){
        if(cows[i] == 1 || cows[i] == 2){
            if(cows[i] == 2) mnCows++;
            break;
        }
    }
    cout << mnCows;

    return 0;
}