import java.util.Scanner;

public class Main {

    private static void printBitArray(boolean[] array, int startIndex) {
        for (int i = startIndex; i < array.length; i++) {
            System.out.print(array[i] ? 1 : 0);
        }
        System.out.println();
    }

    private static void toBitArray(String s, boolean[] bitArray, int padding, int fullLength) {
        for (int i = 0; i < padding - 1; i++) {
            bitArray[i] = true;
        }

        for (int i = padding - 1; i < fullLength; i++) {
            bitArray[i] = s.charAt(i - padding + 1) == '1';
        }
    }

    private static int calculateMinChanges(String input, int originalLength, int windowSize) {
        int minWeight = (windowSize + 1) / 2;
        int fullLength = originalLength + minWeight - 1;
        int changeCount = 0;
        int currentWeight = 0;

        boolean[] bits = new boolean[fullLength];
        toBitArray(input, bits, minWeight, fullLength);

        for (int i = 0; i < windowSize; i++) {
            if (bits[i]) currentWeight++;
        }

        if (currentWeight < minWeight) {
            bits[windowSize - 1] = true;
            currentWeight++;
            changeCount++;
        }

        for (int i = 1; i <= fullLength - windowSize; i++) {
            if (bits[i - 1]) currentWeight--;
            if (bits[i + windowSize - 1]) currentWeight++;

            if (currentWeight < minWeight) {
                bits[i + windowSize - 1] = true;
                currentWeight++;
                changeCount++;
            }
        }

        return changeCount;
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        String s = scanner.next();
        scanner.close();

        int result = calculateMinChanges(s, N, 3);
        System.out.println(result);
    }
}