#include<stdio.h>
int n,m,i,j,e[1001],c[1001],s[5001],r[5001];
int main() {
	freopen("energii.in","r",stdin),freopen("energii.out","w",stdout),scanf("%d%d",&n,&m);
	for(j=1;j<=n;j++) {
		scanf("%d%d",&e[j],&c[j]);
      	for(i=1;i<=m;i++)
        if(j==1)
            s[i]=(i<=e[j]?c[j]:10001);
      	else if(i<=e[j])
            s[i]=r[i]<c[j]?r[i]:c[j];
      	else
            s[i]=r[i]<c[j]+r[i-e[j]]?r[i]:(c[j]+r[i-e[j]]);
      	for(i=1;i<=m;i++)
            r[i]=s[i];
	}
    printf("%d",s[m]!=10001?s[m]:-1);
}