#include <stdio.h>
int main(){
	char c=0;
	int zero_count=0;
	int max_count=0;
	while(scanf("%c",&c)!=EOF){
		if(c=='0'){
			zero_count++;
			max_count = zero_count > max_count ? zero_count : max_count;
		} else {
			zero_count =0;
		}
	}
	printf("%d\n",max_count/2+max_count%2);
	return 0;
}