// yukicoder 884 Eat and Add
// 2019.9.21 bal4u

#include <stdio.h>

#if 1
int getchar_unlocked(void);
#define gc() getchar_unlocked()
#else
#define gc() getchar()
#endif

int ins(char *s) { // 文字列の入力　スペース以下の文字で入力終了
	char *p = s--; int c;
	do c = gc(), *++s = c & 1;
	while (c > ' ');
	return s - p;
}

#define MIN(a,b) ((a)<=(b)?(a):(b))
char N[200005]; int w;

int main()
{
	int i, j, ans;
	
	w = ins(N+1);
	ans = 0, i = w; while (1) {
		while (i > 0 && N[i] == 0) i--;
		if (i == 0) break;
		j = i; while (N[i]) i--;
		j -= i;
		if (i == 0) { ans += MIN(2, j); break; }
		if (j == 1) ans++;
		else if (i > 1 && N[i-1] == 0 && j <= 2) ans += j;
		else ans++, N[i] = 1;
	}
	printf("%d\n", ans);
	return 0;
}