#include <stdio.h>
#include <stdlib.h>

#define DEBUG 0

struct node {
    long int dist;
    long int fuel;
};

int compar1 ( const void * a , const void * b ) {
    long int * x = (long int *) a;
    long int * y = (long int *) b;
    return (*x) - (*y);
}

int compar ( const void * a , const void * b ) {
    struct node * x = (struct node *) a;
    struct node * y = (struct node *) b;
    return (*y).dist - (*x).dist;
}

int main ( int argc , char * argv[] ) {

    int t;
    scanf("%d" , &t);

    while ( t-- ) {

        int n , i;
        scanf("%d" , &n);
        n+=1;

        struct node *list = (struct node*) malloc ( n * (sizeof(struct node) ));
        int *list_fuel = (int*) malloc ( n * (sizeof(int) ));
        int index = -1;

        for ( i = 0 ; i < n ; i++ ) {
            scanf("%ld%ld" , &list[i].dist , &list[i].fuel);
        }
        qsort(list , n , sizeof(struct node) , compar);

        #if DEBUG
        printf("Distance and fuel:\n");
        for ( i = 0 ; i < n ; i++ ) {
            printf("%ld %ld\n" , list[i].dist , list[i].fuel);
        }
        #endif


        long int cur_dist = list[0].dist;
        long int cur_fuel = 0;
        int count = 0;

        for ( i = 0 ; i <= n ; i++ ) {
            cur_fuel -= (cur_dist - list[i].dist);
            cur_dist = list[i].dist;

            while ( cur_fuel < 0 ) {

                if ( index == -1 ) {
                    count = -1;
                    break;
                }

#if DEBUG
                printf("Purchase fuel amount -> %ld\n" , list_fuel[index]);
#endif

                cur_fuel += list_fuel[index--];
                count ++;
            }

            if ( count == -1 ) {
                break;
            }

#if DEBUG
            printf("Adding to list_fuel : %ld\n" , list[i].fuel);
#endif
            list_fuel[++index] = list[i].fuel;
            qsort(list_fuel , index+1 , sizeof(int) , compar1 );

        }
        if ( count > -1 )
            count --;
        printf("%d\n" , count);
    }

    return 0;
}