#include <iostream>
using namespace std;
int main() {
int m; cin >> m;
if (m >= 90) cout << "grade is A";
else if (m >= 80) cout << "Grade is B";
else if (m >= 70) cout << "Grade is C";
else if (m >= 60) cout << "Grade is D";
else cout << "Grade is F";
return 0;
}
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