https://twitter.com/fxn/status/1438891825465528320

bad_elves_2.c

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv) {
    int n = atoi(argv[1]);
    int half = n / 2;
    int i, j;
    int *a = malloc(n * sizeof(int));

    for (j = 0, i = half; i < n   ; i++, j++) a[j] = i;
    for (       i = 0   ; i < half; i++, j++) a[j] = i;

    int start = 0;
    int end = n;
    for (i = n; i > 1; i--) {
        // for (j = start; j < end; j++) printf(" %d", a[j % n]); printf("\n");
        start++;
        if (i & 1)
            a[end++ % n] = a[start++ % n];
    }

    printf("%d\n", a[start % n] + 1);
}