import std;

bool calc(int k, int a, int b) {
    return a <= b / k * k;
}

void main() {
    int k; scan(k);
    int a, b; scan(a, b);
    writeln(calc(k, a, b) ? "OK" : "NG");
}

void scan(T...)(ref T a) {
    string[] ss = readln.split;
    foreach (i, t; T) a[i] = ss[i].to!t;
}
T read(T)() { return readln.chomp.to!T; }
T[] reads(T)() { return readln.split.to!(T[]); }
alias readint = read!int;
alias readints = reads!int;
