题解 | #牛牛学数列#

#include <stdio.h>

int main()
{
    int n = 0;
    int ret = 0;
    scanf("%d",&n);
    for(int i = 0;i<=n;i++)
    {
        if(i%2==0)
        {
            ret = ret-i;
        }
        if(i%2!=0)
        {
            ret = ret+i;
        }
   }
    printf("%d",ret);
    return 0;
}