#include<bits/stdc++.h> using namespace std; #define ioss ios::sync_with_stdio(false),cin.tie(0),cout.tie(0); using ll = long long; using LL = __int128; using ull = unsigned long long; using pii = pair<int, int>; using pll = pair<ll, ll>; using pLL = pair<LL, LL>; using upll = pair<ull, ull>; #define fi first #define se second #define ls i<<1 #define rs i<<1|1 constexpr double eps = 1e-3; const int inf = 0x3f3f3f3f; const ll Inf = 0x3f3f3f3f3f3f3f3f; const int N = 2e5 + 10; const int M = 114514 + 10; const ll mod = 1000000007; const string shiroko; 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;} int x; int main(){ cin>>x; if(x>=90) cout<<"A\n"; else if(x>=80) cout<<"B\n"; else if(x>=70) cout<<"C\n"; else if(x>=60) cout<<"D\n"; else cout<<"F\n"; }