#include<stdio.h>

#define INF -1

typedef struct generator{
	int pow;
	int cost;
};

int main(){

	FILE *f, *g;
	f=fopen("energii.in", "r");
	g=fopen("energii.out", "w");

	generator gen[1001];
	int G, W;
	int cost[20001];

	fscanf(f, "%d %d", &G, &W);
	
	for(int i=0; i<=20000; i++){
		cost[i]=INF;
	}

	cost[0]=0;

	for(int i=0; i<G; i++){
		fscanf(f, "%d %d", &gen[i].pow, &gen[i].cost);
		for(int j=20; j>=gen[i].pow; j--){
			if(cost[j-gen[i].pow]!=-1 && ((cost[j-gen[i].pow]+gen[i].cost>cost[j]) || cost[j]==INF)){
				cost[j]=cost[j-gen[i].pow]+gen[i].cost;
			}
		}
	}
	
	fclose(f);

	int min=99999;
	for(int i=W; i<20000; i++){
		if(cost[i]<min && cost[i]!=INF){
			min=cost[i];
		}
	}

	if(min==99999){
		fprintf(g, "-1");
	}else{
		fprintf(g, "%d", min);
	}
	
	fclose(g);

	return 0;
}