#include <bits/stdc++.h>
using namespace std;
const int siz = 1000000 + 10;
char a[siz];
int main() {
  int t, n, m = 0, i, l, k;
  scanf("%d", &t);
  scanf("%s", a);
  int len = strlen(a);
  int z = 0, o = 0;
  for (l = 0; l < len; l++) {
    if (a[l] == '1')
      o++;
    else if (a[l] == '0')
      z++;
  }
  m = min(o, z);
  len -= (2 * m);
  printf("%d", len);
  return 0;
}
