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#include<stdio.h>

int main(void)

{

         int denominator,flag,i,n;

         double item,sum;

 

         printf("Enter n:");

         scanf("%d",&n);

 

         flag=1;

         denominator=1;

         sum=0;

 

         for(i=1;i<=n;i++){

                   item=flag*1.0/denominator;

                   sum=sum+item;

                   flag=-flag;

                   denominator=denominator+2;

         }

         printf("sum=%f\n",sum);

 

         return 0;

}