#include <bits/stdc++.h> using namespace std; template<typename U, typename V>bool cmin(U &x, const V &y) { return y < x ? x = y, 1 : 0; } template<typename U, typename V>bool cmax(U &x, const V &y) { return y > x ? x = y, 1 : 0; } //不听老人言,磕到甲沟炎 using ll = long long; using pii = pair<int, int>; using ull = unsigned long long; #define fi first #define ls i<<1 #define rs i<<1|1 #define fls i>>1 #define frs i-1>>1 #define endl '\n' #define se second #define int ll const int N = 5e4 + 10, inf = 0x3f3f3f3f; void solve() { int n; cin >> n; if (n>=90)cout <<"A"; else if (n>=80)cout <<"B"; else if (n>=70)cout <<"C"; else if (n>=60)cout <<"D"; else cout <<'F'; } signed main() { ios::sync_with_stdio(0); cin.tie(0), cout.tie(0); int T = 1; //cin >> T; while (T--) { solve(); } return 0; }