#include <stdio.h>
 
int binary_search(int a[], int n, int x) {
    int left = 0;
    int right = n - 1;
    int mid;
 
    while (left <= right) {
        mid = (left + right) / 2;
 
        if (a[mid] == x) {
            return mid;  // 見つかった
        } else if (a[mid] < x) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
 
    return -1;  // 見つからなかった
}
 
int main() {
    int n, x;
    int a[100];
 
    // 要素数入力
    scanf("%d", &n);
 
    // 配列入力（昇順で入れること！）
    for (int i = 0; i < n; i++) {
        scanf("%d", &a[i]);
    }
 
    // 探す値
    scanf("%d", &x);
 
    int ans = binary_search(a, n, x);
 
    if (ans != -1) {
        printf("a[%d] = %d\n", ans, a[ans]);
    } else {
        printf("not found\n");
    }
 
    return 0;
}

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