#include <stdio.h>
#include <bitset>
using namespace std;

const int lim = 100000;
bitset<lim+1> now;

int f(int y)
{
	int l = y-1, r = lim+1;
	while (l + 1 < r){
		int m = (l + r) / 2;
		if ((now >> m).count() >= 1) l = m;
		else r = m;
	}
	return l;
}

int main()
{
	int N; scanf ("%d",&N); while (N--){
		int x,y; scanf ("%d %d",&x,&y);
		int z = f(y);
		if (z >= y) now[z] = 0;

		auto v = ((now << (lim - y)) >> (lim - y + x)) << x;
		now ^= v;
		now ^= (v << 1);
		now[x] = 1;
	}

	printf ("%d\n",now.count());

	return 0;
}