【1336】数列求和3

#include <stdio.h>
#include <stdlib.h>int main()
{int n,i;double m=1.0;double sum,deno=1.0;int sign=1;scanf("%d",&n);for (i=1; i<=n; i++){sum+=sign*m/deno;m++;deno+=2;sign=-sign;}printf("%.3lf\n",sum);return 0;
}