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

char rbuf[1<<20];

#define wt(v) {long _z=v;do*--wp=_z%10+48;while(_z/=10);}

main(){
	long n=read(0,rbuf,sizeof rbuf);
	n-=1;
	char*p0=rbuf;
	char*p1=rbuf+n;
	long a=0,b=*p0;
	while(p0<p1){
		long v0=*p0++;
		long v1=*--p1;
		if(v0!=v1){
			goto owari;
		}
		a|=b^v0;
	}
	if(a){
		n=n==3?-1:n-2;
	}else{
		n=-(n&1);
	}
	if(n<0){
		write(1,"-1",2);
	}else if(n==0){
		write(1,"0",1);
	}else{
		owari:;
		char wbuf[64],*wp=wbuf+sizeof wbuf;
		wt(n);
		write(1,wp,wbuf+sizeof wbuf-wp);
	}
	_exit(0);
}