#include <cstdio>
#include <algorithm>
#define MAXN 5001
#define MAXC 10005
#define IMP 2000000000
#define MAXENG 10001

using namespace std;
FILE *fin=fopen("energii.in","r"),*fout=fopen("energii.out","w");
int e[MAXN],c[MAXN],d[MAXC];
int main(){
    int n,et,s=0;
    fscanf(fin,"%d%d",&n,&et);
    for(int i=1;i<=n;i++){
        fscanf(fin,"%d%d",&e[i],&c[i]);
        s+=e[i];
    }
    if(s<et){
        fprintf(fout,"-1");
        return 0;
    }
    for(int i=1;i<=MAXENG;i++) d[i]=IMP;
    for(int i=1;i<=et;i++){
        for(int j=et;j>=e[i];j--)
        {
            d[j]=min(d[j-e[i]]+c[i],d[j]);
        }
        for(int t=e[i];t>=1;t--)
        {
           d[t]=min(d[t],c[i]);
        }
    }
    fprintf(fout,"%d",d[et]);
    return 0;
}