#include <stdio.h>

#define DATA_LIM 8

int main(void)
{
    double data[DATA_LIM] = {1.0, 3.0, 5.0, 7.0, 9.0, 11.5, 13.0, 15.0};
    int flag;

    for (int i = 0; i < (DATA_LIM - 2); i++)
    {
        if (data[i + 1] - data[i] == data[i + 2] - data[i + 1])
        {
            flag = 1;
        }
        else
        {
            flag = 0;
            break;
        }
    }

    if (flag)
    {
        printf("OK\n");
    }
    else
    {
        printf("NG\n");
    }

    return 0;
}