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,x; 20 int main() { 21 memset(dp,INF,sizeof(dp)); 22 v.push_back(0); 23 while(~scanf("%d",&x))v.push_back(x); 24 dp[1]=0; 25 n=v.size()-1; 26 for(int i=1; i<=n; i++) { 27 if(dp[i]==INF)continue; 28 for(int j=1; j<=v[i]&&i+j<=n; j++) { 29 dp[i+j]=min(dp[i+j],dp[i]+1); 30 } 31 } 32 if(dp[n]==INF)printf("-1\n"); 33 else printf("%d\n",dp[n]); 34 return 0; 35 } 