#includeint main(){ int i,j; double add = 0; printf("Please input a number!"); scanf("%d",&i); for(j = 0;j < i;j++) { if(j%2) add -= 1 / (double)(1 + j * 3); else add += 1 / (double)(1 + j * 3); } printf("The result is %f",add); return 0;}