/*

	1/1-1/2+1/3-1/4+...1/n;

	*/

	int n = 1;

	double sum = 0;

	double frac = 0;

	int i = 1;

	scanf_s("%d", &n);

	while (i < (n + 1))  //1到n

	{

		if (i % 2 == 0)

		{

			frac = -1.0 / i;

		}

		else

		{

			frac = 1.0 / i;

		}

		sum = sum + frac;

		i++;

	}

	printf("sum is %f", sum);

#define N 3

int main(void)

{

    double data;

    int i;

    double sum = ;

    int mul=;

    for (i = ; i < N; i++,mul*=-)

    {

        data = 1.0 / (i + );

        data = data * mul;

        sum = sum + data;

    }

    printf("%f",sum);

    return ;

}