1 #define mm(a) memset(a,0,sizeof(a));
 2 #define max(x,y) (x)>(y)?(x):(y)
 3 #define min(x,y) (x)<(y)?(x):(y)
 4 #define Fopen freopen("1.in","r",stdin); freopen("m.out","w",stdout);
 5 #define rep(i,a,b) for(int i=(a);i<=(b);i++)
 6 #define per(i,b,a) for(int i=(b);i>=(a);i--)
 7 #include<bits/stdc++.h>
 8 typedef long long ll;
 9 #define PII pair<ll,ll>
10 using namespace std;
11 const int INF=0x3f3f3f3f;
12 const int MAXN=(int)2e5 + 5;
13 const ll mod=1e9+7;
14 
15 
16 string input,temp;
17 vector<int>v;
18 map<int,int>mp;
19 int n,dp[MAXN],m;
20 int main() {
21     while(cin>>input) {
22         istringstream iss(input);
23         memset(dp,INF,sizeof(dp));
24         v.clear();
25         v.push_back(0);
26         while (getline(iss, temp, ‘,‘)) {
27             int x=atoi(temp.c_str());
28             v.push_back(x);
29         }
30         dp[1]=0;
31         n=v.size()-1;
32         for(int i=1; i<=n; i++) {
33             if(dp[i]==INF)continue;
34             for(int j=1; j<=v[i]&&i+j<=n; j++) {
35                 dp[i+j]=min(dp[i+j],dp[i]+1);
36             }
37         }
38         if(dp[n]==INF)printf("-1\n");
39         else printf("%d\n",dp[n]);
40     }
41     return 0;
42 }