#include <stdio.h>
#include <algorithm>

using namespace std;

#define ll long long unsigned
#define pb push_back
#define mp make_pair

int EG[1005],CG[1005],dp[5005];
// dp[i] = pretul minim pt a produce i energie
const int MX = 1e7;

int main(){
    int G,W,i,j;
    freopen("energii.in", "r", stdin);
    freopen("energii.out", "w", stdout);
    scanf("%d",&G);
    scanf("%d",&W);
    for(i = 1;i <= G;i++){
        scanf("%d %d",&EG[i],&CG[i]);
    }
    for(i = 1;i <= W+1;i++){
        dp[i] = MX;
    }
    for(i = 1;i <= G;i++){
        for(j = W-EG[i];j >= 0;j--){
            dp[j+EG[i]] = min(dp[j+EG[i]],dp[j]+CG[i]);
        }
        for(j = EG[i];j >= 0;j--){
            dp[j] = min(CG[i], dp[j]);
        }
    }
    if(dp[W] == MX){
        printf("-1");
    }else{
        printf("%d",dp[W]);
    }
    return 0;
}