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

typedef unsigned long ulong;

ulong f1(){
	char*mmap();
	char*rp=mmap(0l,1l<<25,1,2,0,0ll);
	while(*rp++!=10);
	long a1=0,a9=0,z=0;
	for(long c;c=*rp++,c>='0';){
		if(c=='1'){
			++a1;
		}else if(c=='9'){
			if(a1){
				--a1;
				++z;
			}else{
				++a9;
			}
		}else{
			++z;
		}
	}
	return z+(a9>>=1,a1>=a9?a9+(a1-a9>>1):a1);
}

void f2(ulong z){
	char wbuf[64],*wp=wbuf+sizeof wbuf;
	do*--wp=z%10+48;while(z/=10);
	write(1,wp,wbuf+sizeof wbuf-wp);
	_exit(0);
}

int main(){
	f2(f1());
	return 0;
}