#include using namespace std; int main() { long n,i,j,c,inf=100000; cin >> n; vector a(n,0),ans(n+1,inf); for(i=1; i=(1<=1; j--){ if(j+a[j]<=n && ans[j+a[j]]!=inf){ ans[j]=min(ans[j],ans[j+a[j]]+1); } if(j-a[j]>=1 && ans[j-a[j]]!=inf){ ans[j]=min(ans[j],ans[j-a[j]]+1); } } } /* for(i=1; i<=n; i++){ cout << ans[i] << ' '; } cout << endl; */ if(ans[1]==inf){ cout << -1 << endl; }else{ cout << ans[1] << endl; } return 0; }