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

class cow {
	public:
		int milk, time;
} cows[10010];

bool cmp(const cow& a, const cow& b) {
	if (a.milk == b.milk)
		return a.time < b.time;
	return a.milk > b.milk;
}

int* freq;

void update(int val, int pos) {
	while (pos <= 10010) {
		freq[pos] += val;
		pos += (pos & (-pos));
	}
}

int query(int pos) {
	int ans = 0;
	while (pos > 0) {
		ans += freq[pos];
		pos -= (pos & (-pos));
	}
	return ans;
}

int main(void) {
	int n;
	scanf("%d", &n);
	freq = (int*) calloc(10010, sizeof(int));
	int mt = 0;
	for (int i = 0; i < n; i++) {
		scanf("%d %d", &cows[i].milk, &cows[i].time);
		mt = max(mt, cows[i].time);
	}
	sort(cows, cows+n, cmp);
	//for (int i = 0; i < n; i++) {
	//	printf("%d %d\n", cows[i].milk, cows[i].time);
	//}
	int count = 0, id = 0;
	int ans = 0, allowed = 0;
	while (count < mt && id < n) {
		if (query(cows[id].time) < cows[id].time) {
			ans += cows[id].milk;
			update(1, cows[id].time);
			count++;
		}
		id++;
	}
	printf("%d\n", ans);
	return 0;
}