#include <stdio.h>

// Function to check if a number is even
int isEven(int num) {
    return num % 2 == 0;
}

// Function to find the maximum number of contiguous subarrays with even sum
int maxContiguousSubarrays(int arr[], int N) {
    int count = 0, even_sum = 0;
    
    for (int i = 0; i < N; i++) {
        // If the current element is odd, we need to increment the count of even sums
        if (!isEven(arr[i]))
            even_sum++;
        // If the number of odd elements encountered so far is even, we can form a subarray
        if (even_sum % 2 == 0)
            count++;
    }
    
    // If the total count of odd elements is even, we can form subarrays ending with the last element
    if (even_sum % 2 == 0)
        return count;
    else
        return -1;
}

int main() {
    int N;
    scanf("%d", &N);
    
    int arr[N];
    for (int i = 0; i < N; i++)
        scanf("%d", &arr[i]);
    
    printf("%d\n", maxContiguousSubarrays(arr, N));

    return 0;
}