#include <iostream>
#include <limits>
#include <cstdio>
#define NMAX 10000
using namespace std;

int G, W, E[NMAX], C[NMAX], Sol[NMAX][NMAX];

void read(void)
{
	FILE *f = fopen("energii.in", "r");
	fscanf(f, "%d", &G);
	fscanf(f, "%d", &W);
	for(int i = 1; i <= G; ++i)
		fscanf(f, "%d%d", &E[i], &C[i]);

	fclose(f);
}

void solve(void)
{
	for(int i = 1; i <= W; ++i)
		Sol[0][i] = 10000;
	
	
	for(int i = 1; i <= G; ++i)
		for(int j = 1; j <= W; ++j)
			if(E[i] <= j && Sol[i-1][j - E[i]] + C[i] < Sol[i-1][j])
				Sol[i][j] = Sol[i-1][j - E[i]] + C[i];
			else
				if(Sol[i-1][j] > C[i] && E[i] > j)
					Sol[i][j] = C[i];
				else
					Sol[i][j] = Sol[i-1][j];
				
}

void print(void)
{
	FILE *g = fopen("energii.out", "w");
	if(Sol[G][W] == 10000)
		fprintf(g, "-1\n");
	else
		fprintf(g, "%d\n", Sol[G][W]);
	
	fclose(g);	
}
int main(void)
{
	read();
	solve();
	print();
	
	return 0;
}