grades.cpp

// NOTE: it is recommended to use this even if you don't understand the following code.

#include <iostream>
#include <fstream>

using namespace std;

int main() {
//  uncomment the following lines if you want to read/write from files
//  ifstream cin("input.txt");
//  ofstream cout("output.txt");
	
	int N;
    cin >> N;
    
    int G[N];
    for(int i=0; i<N; i++)
        cin >> G[i];

    // insert your code here
    int start=0, end=N-1, ans;
    while (G[start] >= 6 && start != N) {
    	start ++;
	}
	
	if (start >= N-1) {
		ans = -1;
	} else {
		while (G[end] < 6 && end != start && end != 0) {
			end --;
		}
		if (end != start) {
			ans = end - start +1;
		} else {
			ans = -1;
		}
		
	}
    
    cout << ans << endl; // print the result
    return 0;
}