#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    int n = 10;
    int k = 3;
    int prefix[n];
    prefix[0] = arr[0];
    for (int i = 1; i < n; i++) {
        prefix[i] = prefix[i - 1] + arr[i];
    }
    int total = 0;
    for (int i = 0; i <= n - k; i++) {
        int sum;
        if (i == 0)
            sum = prefix[k - 1];                   
        else
            sum = prefix[i + k - 1] - prefix[i - 1];  

        total += sum;
    }

    printf("Sum of all subarray sums: %d\n", total);
    return 0;
}