44.求多项式

#include<stdio.h>
int main()
{
    int n,i,sum;
    while(scanf("%d",&n)!=EOF){
        sum=0;
    for(i=1;i<=n;i++){
        if(i%2==0)
        sum=sum-i;
        else
        sum=sum+i;
    }
        printf("%d\n",sum);
    }
    return 0;
}