/******************************************************************************
 *  Name:    Kevin Wayne
 *  NetID:   wayne
 *  Precept: P00
 *
 *  Description:  Computes the G-statistic of the observed frequencies
 *                and the expected frequencies.
 ******************************************************************************/

public class GStatistic {

    public static void main(String[] args) {

        double gStatistic = 0.0;
        int numberOfNonzeros = 0;

        // read data from standard input and update statistics
        int n = StdIn.readInt();
        for (int i = 0; i < n; i++) {
            int x = StdIn.readInt();
            int y = StdIn.readInt();
            if (y != 0) numberOfNonzeros++;
            if (x != 0) gStatistic += 2.0 * x * Math.log(1.0 * x / y);
        }

        // print results to standard output
        int degreesOfFreedom = numberOfNonzeros - 1;
        System.out.printf("degrees of freedom = %d\n", degreesOfFreedom);
        System.out.printf("G-statistic        = %.4f\n", gStatistic);
    }
}