#pragma comment(linker, "/STACK:102400000, 102400000")#include<cstdio>#include<cstring>#include<cstdlib>#include<cctype>#include<cmath>#include<iostream>#include<sstream>#include<iterator>#include<algorithm>#include<string>#include<vector>#include<set>#include<map>#include<stack>#include<deque>#include<queue>#include<list>#define Min(a, b) ((a < b) ? a : b)#define Max(a, b) ((a < b) ? b : a)const double eps = 1e-8;inline int dcmp(double a, double b){    if(fabs(a - b) < eps) return 0;    return a > b ? 1 : -1;}typedef long long LL;typedef unsigned long long ULL;const int INT_INF = 0x3f3f3f3f;const int INT_M_INF = 0x7f7f7f7f;const LL LL_INF = 0x3f3f3f3f3f3f3f3f;const LL LL_M_INF = 0x7f7f7f7f7f7f7f7f;const int dr[] = {0, 0, -1, 1, -1, -1, 1, 1};const int dc[] = {-1, 1, 0, 0, -1, 1, -1, 1};const int MOD = 1e9 + 7;const double pi = acos(-1.0);const int MAXN = 10000 + 10;const int MAXT = 10000 + 10;using namespace std;int N, L, P;struct Node{    int d, fuel;    Node(){}    void read(){        scanf("%d%d", &d, &fuel);    }    void Set(int dd, int ff){        d = dd;        fuel = ff;    }    bool operator < (const Node& rhs)const{        return d > rhs.d;    }}num[MAXN];priority_queue<int> q;int solve(){    int ans = 0;    for(int i = 1; i <= N + 1; ++i){        int tmp = num[i - 1].d - num[i].d;        if(P - tmp >= 0) P -= tmp;        else{            while(!q.empty() && P - tmp < 0){                P += q.top();                q.pop();                ++ans;            }            if(P - tmp < 0) return -1;            P -= tmp;        }        q.push(num[i].fuel);    }    return ans;}int main(){    scanf("%d", &N);    for(int i = 1; i <= N; ++i){        num[i].read();    }    scanf("%d%d", &L, &P);    sort(num + 1, num + 1 + N);    num[0].Set(L, 0);    num[N + 1].Set(0, 0);    printf("%d\n", solve());    return 0;}