#include <bits/stdc++.h>

using namespace std;

int dp[1001][5001];
int Eg[1001],Cg[1001];

int W,G;
const int inf = 1e7;

int main()
{
    freopen("energii.in","r",stdin);
    freopen("energii.out","w",stdout);
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    cin >> G >> W;
    for(int i = 1;i <= G; ++i)
        cin >> Eg[i] >> Cg[i];
    for(int i = 0;i <= G; ++i)
        for(int j = 1;j <= W; ++j)
            dp[i][j] = inf;
    for(int i = 1;i <= G; ++i){
        for(int j = 1;j <= W; ++j){
            dp[i][j] = dp[i-1][j];
            if(Eg[i] >= j)
                dp[i][j] = min(dp[i][j] , Cg[i]);
            else dp[i][j] = min(dp[i][j] , dp[i-1][j-Eg[i]] + Cg[i]);
        }
    }
    cout << (dp[G][W] == inf ? -1 : dp[G][W]);
}