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

char*mmap();

int a[400001];

main(){
	char*rp=mmap(0l,200001l,1,2,0,0ll);
	int d=200000;
	int i=1;
	int m=0;
	int c;
	do{
		if(a[d]){
			if(m<i-a[d]){
				m=i-a[d];
			}
		}else{
			a[d]=i;
		}
		d+=(*rp++&2)-1;
		++i;
	}while(*rp);
	printf("%d",m);
}