some C++ question

so /prog/rammers can you tell me why this only returns
x=1 y=1
I'm trying to have it return the values that equal 133745639

heres the code:

#include <cstdlib>
#include <iostream>

using namespace std;

int main(int argc, char* argv[])
{
unsigned long int x = 1;
unsigned long int y = 1;
unsigned long int z;


while ( z != 133745639)
{
z = x * y ;

if ( z = 133745639 )
{
cout << "x=" << x << "y=" << y << endl;
}
else
x++;
}
system("PAUSE");
return 0;

}

ASSIGNMENT: x := 5
EQUALITY: if x = 5

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