#include<stdio.h>
int n,m,i,j,e,c,s[5001],r[5001];
int main() {
	freopen("energii.in","r",stdin),freopen("energii.out","w",stdout),scanf("%d%d",&n,&m);
	for(j=0;j<n;j++) {
		scanf("%d%d",&e,&c);
      	for(i=1;i<=m;i++)
            s[i]=(!j?(i<=e?c:10001):(r[i]<c+(i>e?r[i-e]:0)?r[i]:(c+(i>e?r[i-e]:0)))),r[i]=s[i];
	}
    printf("%d",s[m]!=10001?s[m]:-1);
}