#define DM 5005
#define inf 0x3f3f3f3f
#include <cstring>
#include <fstream>
using namespace std;

ifstream fi ("energii.in");
ofstream fo ("energii.out");
int n, w, dp[DM], a, b;

int main()
{
    fi >> n >> w;
    memset(dp, inf, sizeof(dp));
    dp[0] = 0;
    for (int i = 1; i <= n; ++i)
    {
        fi >> a >> b;
        for (int j = w; j >= 1; --j)
        {
            if (a >= j)
                dp[j] = min(dp[j], b);
            else if (dp[j-a] != inf)
                dp[j] = min(dp[j+1], min(dp[j], dp[j-a] + b));
        }
    }
    if (dp[w] != inf)
        fo << dp[w];
    else
        fo << -1;
    return 0;
}