#include <iostream>
#include <string.h>
#include <algorithm>

using namespace std;

struct gen {
	int e;
	int c;
};

int best[5010];

int g, w;

int main (void) {
	freopen("energii.in", "r", stdin);
	freopen("energii.out", "w", stdout);
	
	scanf("%d", &g);
	scanf("%d", &w);
	
	//read
	gen elem;
	memset(best, 999999, (w+1) * sizeof(int));
	
	for (int j = 0; j < g; ++j) {
		scanf("%d %d", &elem.e, &elem.c);
			for (int i = w; i >=1 ; --i) {
				if (elem.e >= i) {
					best[i] = min(best[i], elem.c);
				} else {
					best[i] = min(best[i - elem.e] + elem.c, best[i]);
				}
			}
	}
	
	if (best[w] == 9999999) {
		printf("-1");
	} else {
		printf("%d", best[w]);
	}
	
	return 0;
}