/*

     找规律/贪心：ans = n - 01匹配的总数，水

 */

 #include <cstdio>

 #include <iostream>

 #include <algorithm>

 #include <cstring>

 #include <cmath>

 using namespace std;

 const int MAXN = 2e5 + ;

 const int INF = 0x3f3f3f3f;

 char s[MAXN];

 int main(void)        //Codeforces Round #310 (Div. 2) A. Case of the Zeros and Ones

 {

     // freopen ("A.in", "r", stdin);

     int n;

     while (scanf ("%d", &n) == )

     {

         scanf ("%s", s);

         int cnt_0 = , cnt_1 = ;

         for (int i=; i<n; ++i)

         {

             if (s[i] == '')    cnt_0++;

             else    cnt_1++;

         }

         printf ("%d\n", n - min (cnt_0, cnt_1) * );

     }

     return ;

 }