11057.cpp

#include <bits/stdc++.h>

int main() {
    int a[10001];
    int i, j, n, t, m, path, max, min;
    while (scanf("%d", &t) == 1) {
        for (i = 0; i < t; i++) scanf("%d", &a[i]);

        scanf("%d", &m);
        std::sort(a, a + t);
        min = i = 0;
        max = j = t - 1;
        path = a[j] - a[i];
        while (1) {
            while (a[i] + a[j] > m) {
                j--;
            }
            while (a[i] + a[j] < m) {
                i++;
            }
            if (a[i] + a[j] == m && (a[j] - a[i] <= path) && i != j) {
                max = j;
                min = i;
                path = a[j] - a[i];
                i++;
            }
            if (j <= i) break;
        }
        if (max < min) {
            i = max;
            max = min;
            min = i;
        }
        printf("Peter should buy books whose prices are %d and %d.\n\n", a[min], a[max]);
    }
    return 0;
}