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

int main() {
    int top = 999999999;

    char *a;
    a = (char*) calloc(top+1, sizeof(char));
    unsigned int sum = 0;

    for (int i=0; i<10; ++i) {
        int m, k;
        // (tested with cc -O3 t.c && /usr/bin/time -lp ./a.out)
        // (cc is Apple LLVM version 7.0.0)

        // This code ran in ~0.90 seconds on my system
//        char *b = a + top;
//        a++;
//        for (; a < b; )
//        {
//            sum += ( *a++ ) * ( *b--);
//        }

        // This code ran in ~5 seconds on my system
        for (m = 1, k = top; m < k; ++m, --k) {
            // Here is the bottle neck!!
            sum += a[m]*a[k];
        }
    }
    printf("%d\n", sum);
}