#include <bits/stdc++.h>

using namespace std;

ifstream fin("energii.in") ;
ofstream fout("energii.out") ;

int dp[5005][5005] ;
int e[1005] , c[1005] ;

int main()
{
    int i , j , g , w , s = 0 ;
    fin >> g >> w ;
    for ( i = 1 ; i <= g ; i++ )
    {
        fin >> e[i] >> c[i] ;
        s = s+e[i] ;
    }
    if ( s < w )
    {
        fout << "-1" ;
        return 0 ;
    }
    for ( i = 1 ; i <= w ; i++ )
        dp[0][i] = 0x3f3f3f3f ;
    for ( i = 1 ; i <= g ; i++ )
    {
        for ( j = 1 ; j <= w ; j++ )
        {
            if ( j-e[i] >= 0 )
                dp[i][j] = min(dp[i-1][j],dp[i-1][j-e[i]] + c[i]) ;
            else
                dp[i][j] = min(dp[i-1][j],c[i]) ;
        }
    }
    fout << dp[g][w] ;
}