include <stdio.h>

include <math.h>

int main()
{
int t, a=0, b=0, sum;
char g[101];
scanf("%d", &t);
getchar();
scanf("%s", g);
int l=strlen(g);
for(int i=0;i<l;i++)
{
if(g[i]=='x') a++;
else b++;
}
//printf("%d %d\n", a, b);
sum=fabs((a-b)/2);
printf("%d\n", sum);

return 0;

}