1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <iostream>
 5 using namespace std;
 6 #define inf 999999999
 7 
 8 int a[22];
 9 char c[22];
10 int n;
11 
12 
13 int dfs(int k,int step){
14 
15     if(k>=n){
16         return a[k-1]?inf:step;
17         
18     }
19     if(a[k-1]){          //若第K张牌前面一张牌为反面，那么需要翻第k张牌使得第k-1张牌正面朝上 
20         a[k-1]=0;
21         a[k]=!a[k];
22         a[k+1]=!a[k+1];
23             step++;
24     }
25     return dfs(k+1,step);
26 }
27 
28 main()
29 {
30     int i, j;
31     while(scanf("%s",c)!=EOF){
32          n=strlen(c);
33          for(i=0;i<n;i++) a[i]=c[i]-‘0‘;
34          a[0]=!a[0];a[1]=!a[1];            //翻第一张牌 
35          int num=inf;
36          
37          num=min(num,dfs(1,1));      
38          for(i=0;i<n;i++) a[i]=c[i]-‘0‘; 
39          num=min(num,dfs(1,0));          //不翻第一张牌 
40          if(num==inf) printf("NO\n");
41          else printf("%d\n",num); 
42     }
43 }