#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

#define getrp() ({char*mmap();mmap(0l,1l<<25,1,2,0,0ll);})
#define rd() ({long _v=0,_c;while(_c=*rp++-48,_c>=0)_v=_v*10+_c;_v;})
#define wt(v) ({ulong _z=v;do*--wp=_z%10+48;while(_z/=10);})
#define wt1(v) ({char wbuf[64],*wp=wbuf+sizeof wbuf;wt(v);write(1,wp,wbuf+sizeof wbuf-wp);})

typedef unsigned long ulong;

int main(){
	char*rp=getrp();
	long n=rd();
	char*s=rp;
	char*e=s+n;
	char*t=e+1;
	long a=0,b=0;
	while(*s!=10){
		a+=*s++^*t;
		b+=*--e^*t;
		++t;
	}
	wt1(a&1?b:a);
	_exit(0);
}