oj 3

#include<stdio.h>
 #include<math.h> 
main() 
{  
    int flag,i,n;  
    double item,sum; 
 printf("Enter n:");  
 scanf("%d",&n);
 flag=1;  
 sum=0;  
 for(i=1;i<=n;i++){  
     item=flag*(1.0/(3*i-2)); 
     sum=sum+item;   
     flag=-flag; 
 }  
printf("sum=%.5f\n",sum); 
}