The trip

#include <stdio.h>
#include <assert.h>

int main() {

    int debug = 0;
    int n;

    while (scanf("%d", &n) != EOF) {
        if (n == 0) break;
        long amount[n];
        long total = 0;
        long average = 0;
        long diff = 0;
        for (int i = 0; i < n; i ++) {
            double temp;
            scanf("%lf", &temp);
            temp *= 1000;
            amount[i] = temp;
            if (debug) printf("spend %d, %ld\n", i, amount[i]);
            total += temp;
        }
        // get average of input amounts
        average = total / n;
        if (debug) printf("average=%ld\n", average);
        long negdiff = 0;
        long posdiff = 0;
        for (int i = 0; i < n; i ++) {
            diff = (amount[i] - average)/10;
            if (diff < 0) {
                negdiff += diff;
            } else {
                posdiff += diff;
            }
        }
        long exchange = (-negdiff > posdiff) ? -negdiff : posdiff;
        printf("$%ld.%02ld\n", exchange/100, exchange%100);
    }
    return 0;
}