#include <bits/stdc++.h>
using namespace std;
 
int binarySearch(vector<int> a, int low, int high, int x)
{
    while (low <= high) {
        int mid = low + (high - low) / 2;
        if (a[mid] == x)
            return mid;
        if (a[mid] < x)
            low = mid + 1;
        else
            high = mid - 1;
    }
    return -1;
}
 
int main()
{
    int n; cin >> n;
    vector<int> a(n);
    for(int i=0; i<n; i++){
        cin >> a[i];
    }
    cout << binarySearch(a, 0, n-1, 5);
}
 

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5
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