#include <cstdio>
#include <algorithm>
#include <iostream>
#define inf 20000000
using namespace std;

int g;
int w;
int e[1005];
int c[1005];
int dp[1005][5005];

int main()
{
    int g,w;
    freopen("energii.in","r", stdin);
    freopen("energii.out","w", stdout);
    scanf("%d %d",&g,&w);
    for(int i=1;i<=g;i++)
        scanf("%d %d",&e[i],&c[i]);
    for(int i=0;i<=g;i++)
        for(int j=0;j<=w;j++)
            dp[i][j]=inf;

    for(int i=1;i<=g;i++)
        for(int j=1;j<=w;j++)
        {
            if(j<=e[i])
                dp[i][j]=min(dp[i-1][j],c[i]);

            else
                dp[i][j]=min(dp[i-1][j],dp[i-1][j-e[i]]+c[i]);
        }

    if(dp[g][w]==1<<30)
        printf("-1");
    else
        printf("%d",dp[g][w]);
    return 0;
}