C++ :

#include <cstdio>
#include <cstring>
#include <queue>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long ll;

int N, C, F;
pair<int,int> a[200100];
ll c[200100], d[200100];
priority_queue<int> Q;

int main()
{
	//freopen("money.in","r",stdin);
	//freopen("money.out","w",stdout);
	while(scanf("%d%d%d",&N,&C,&F) != EOF){
		for(int i = 1;i <= C; ++i) scanf("%d%d",&a[i].first,&a[i].second);
		sort(a + 1,a + 1 + C);
		memset(c, 0, sizeof(c));
		while(!Q.empty()) Q.pop();
		ll sum = 0ll;
		for(int i = 1;i <= N/2; ++i){
			Q.push(a[i].second);
			sum += 1ll*a[i].second;
		}
		for(int i = N/2 + 1;i <= C; ++i){
			c[i] = sum;
			if(Q.empty()) continue;
			if(Q.top() > a[i].second){
				sum = sum - Q.top() + a[i].second;
				Q.pop();
				Q.push(a[i].second);
			}
		}
		while(!Q.empty()) Q.pop();
		sum = 0ll;
		for(int i = C;i >= C - N/2 + 1; --i){
			Q.push(a[i].second);
			sum += 1ll*a[i].second;
		}
		for(int i = C - N/2;i >= 1; --i){
			d[i] = sum;
			if(Q.empty()) continue;
			if(Q.top() > a[i].second){
				sum = sum - Q.top() + a[i].second;
				Q.pop();
				Q.push(a[i].second);
			}
		}
		int ans = -1;
		for(int i = N/2 + 1;i <= C - N/2; ++i)
			if(a[i].second + c[i] + d[i] <= F) ans = max(ans, a[i].first);
		printf("%d\n",ans);
	}
}