void lab4(int k)
{
int num_threads=k;
 static long num_steps=100000000;
 double sum,pi,x,step;
float start=omp_get_wtime();
omp_set_num_threads(num_threads);
pi=0.0;
 #pragma omp parallel
{

 int i;
int tid;
tid=omp_get_thread_num();
double x;
 double sum=0.0;
 step=1.0/(double)num_steps;
   for(i=tid;i<num_steps;i=i+num_threads)
    {
     x=(i+0.5)*step;
     sum=sum+4.0/(1+x*x);
    }

#pragma omp critical
{
 pi=pi+sum*step;
}
}
float end=omp_get_wtime();
        float secs=end-start;
        printf("pi=%f time=%f threads=%d\n",pi,secs,num_threads);
}