#include<cstdio>

int g, w, i, j, x, y, min, en[1100], cost[1100];

int main () {
    freopen("energii.in", "r", stdin);
    freopen("energii.out", "w", stdout);
    scanf("%d %d", &g, &w);

    en[0]=0; cost[0]=0;
    for (i=1; i<=g; i++) {
        scanf("%d %d", &x, &y);
        en[i]=en[i-1]+x;
        cost[i]=cost[i-1]+y;
    }
    min=10200;
    for (i=1; i<=g; ++i)
        for (j=0; j<=i-1; ++j)
          if (en[i]-en[j]>=w && cost[i]-cost[j]<=min) min=cost[i]-cost[j];
    if (min==10200) min=-1;
    printf("%d", min);
    return 0;
}