#include <bits/stdc++.h>
using namespace std;
int main() {
// your code goes here
int n;
cin>>n;
int a[n],i,l,r;
for(i=0;i<n;i++)
cin>>a[i];
int jumps[n+1]={0};
for(i=1;i<=n;i++){
l=max(1,i-a[i-1]);
r=min(n,i+a[i-1]);
jumps[l]=max(jumps[l],r-l);
}
i=jumps[0];
int score=0;
while(i<n-1){
i+=jumps[i];
score++;
}
cout<<score;
return 0;
}
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