#include <bits/stdc++.h>
#define For(i, a, b) for(int (i)=(int)(a); (i)<(int)(b); ++(i))
#define rFor(i, a, b) for(int (i)=(int)(a)-1; (i)>=(int)(b); --(i))
#define rep(i, n) For((i), 0, (n))
#define rrep(i, n) rFor((i), (n), 0)
#define fi first
#define se second
using namespace std;
typedef long long lint;
typedef unsigned long long ulint;
typedef pair<int, int> pii;
typedef pair<lint, lint> pll;
template<class T> bool chmax(T &a, const T &b){if(a<b){a=b; return true;} return false;}
template<class T> bool chmin(T &a, const T &b){if(a>b){a=b; return true;} return false;}
template<class T> T div_floor(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>=0 ? a/b : (a+1)/b-1;
}
template<class T> T div_ceil(T a, T b){
    if(b < 0) a *= -1, b *= -1;
    return a>0 ? (a-1)/b+1 : a/b;
}

constexpr lint mod = 1000000007;
constexpr lint INF = mod * mod;
constexpr int MAX = 100010;

int main(){
    int n;
    scanf("%d", &n);
    int nxt[20][n];
    rep(i, n){
        int p;
        scanf("%d", &p);
        nxt[0][i] = i + p;
    }
    For(k, 1, 20)rep(i, n) nxt[k][i] = nxt[k-1][nxt[k-1][i]];

    int d[n];
    fill(d, d+n, mod);
    queue<int> que;
    d[0] = 0;
    que.push(0);
    while(!que.empty()){
        int v = que.front();
        que.pop();
        For(i, 1, 7){
            if(v + i >= n-1){
                printf("%d\n", d[v] + 1);
                return 0;
            }
            int nv = nxt[19][v + i];
            if(nxt[0][nv] != nv) continue;
            if(nv == n-1){
                printf("%d\n", d[v] + 1);
                return 0;
            }
            if(chmin(d[nv], d[v] + 1)) que.push(nv);
        }
    }
}
