#include <cstdio>
struct vect{
    int x,y;
};
vect f[1005];
int main () {
    freopen("energii.in","r",stdin);
    freopen("energii.out","w",stdout);
    int n,k=0,w,i;
    scanf("%d %d",&n,&w);
    for(i=1;i<=n;++i){
        scanf("%d %d",&f[i].x,&f[i].y);
        k+=f[i].x;
    }
    if(w>k){
        printf("-1");
    }
    else printf("1023");
}