int possion(int Lambda) 
{ 
int  k = 0;
long double p = 1.0; 
long double l = exp(-Lambda);         
srand((unsigned)time(NULL));         
//printf("%1.5Lf\n", l); 
while(p>=l) 
{ 
double u = U_Random(); 
p *= u; k++; 
} 
return k-1; 
}

double U_Random() 
{ 
double f; 
f = (float)(rand() %100);
return f/100; 
}

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