The Wrong Finish Time

This is meant to be earliest-finish interval scheduling. The classes arrive already sorted by finish time.

int schedule(const vector<int>& start, const vector<int>& finish) {
    int n = start.size();
    int count = 1;                       // class 0 is always taken
    for (int i = 1; i < n; i++) {
        if (start[i] >= finish[i - 1])   // compare against the previous class
            count++;
    }
    return count;
}

Which input makes it return fewer classes than the optimum? Each input is a list of (start, finish) pairs, already sorted by finish.