#include <stdio.h>

int main()
{
    int n=0,w=0,i=0,s=0,x=0,y=0;
    freopen("energii.in","r",stdin);
    freopen("energii.out","w",stdout);
    scanf("%d%d",&n,&w);
    for (i=0; i<n; ++i)
    {
        scanf("%d%d",&x,&y);
        s+=x;
        if (s>w) {y=-13;break;}
    }
    if (y!=-13) printf("-1");
    return 0;
}