#include <stdio.h>
#include <stdlib.h>
#define min(a,b) (a < b? a : b)
#define MAX 10001
#define CAP_MAX 10001
#define INFINITE 1000001
int n, W;
int energie[MAX], cost[MAX];
int v[2][MAX];

void readInput (){
    int i;
    FILE *f= fopen("energii.in","r");
    fscanf(f,"%d%d", &n,&W);
    for (i = 1; i <= n; i++)
        fscanf(f,"%d%d", &energie[i],&cost[i]);
}
void run ()
{
    int i, j, k;
    FILE *g= fopen("energii.out","w");
    for ( j=1; j<=W; j++)
        v[0][j]=INFINITE;
    for ( i = 1; i <= n; i++){
        for ( j = 1; j <= W; j++){
            v[1][j] = v[0][j];
            if ( energie[i] <= j )
                 v[1][j]= min(v[1][j],v[0][j - energie[i]]+ cost[i]);
        }

        for ( k = 1; k <= W; k++)
            v[0][k]=v[1][k];
    }
    if( v[1][W] != INFINITE)
        fprintf(g,"%d", v[1][W]);
    else fprintf(g,"-1");
}
int main()
{
    readInput();
    run();
    return 0;
}