#include#include #include using namespace std; bool solve(vector v){ int maxp = 0; for ( int i = 0; i < v.size(); i++ ){ if ( i*10 <= maxp ){ maxp = max(maxp, v[i] + i*10); } else return false; } return 10*(v.size()-1) <= maxp; } main(){ int N; cin >> N; vector v, u; for ( int i = 0; i < N; i++ ){ int x; cin >> x; v.push_back(x); } u = v; reverse(u.begin(), u.end()); cout << (solve(v)&&solve(u)?"yes":"no") << endl; return 0; }