PTA-计算圆周率

#includeint main()

{

double n,i=1,mul=1;

double t=1,y=1.0,a,sum=1;

scanf("%lf",&a);

for(n=1;t>a;n++){

y=y*n;

mul=mul*(2*n+1);

t=y/mul;

sum=sum+t;

}

// printf("%f,%d\n",t,n);

printf("%.6f",sum*2);

return 0;

}