http://i.stack.imgur.com/eIggZ.png every resistance is of 1 ohm

Hint - there's interesting symmetry going on around R3. Suppose R3 was infinite - what would the equivalent resistance for the circuit be? Now suppose R3 is 0 - again, what would the equivalent resistance be?

Or you can do it the hard way. Assume a voltage across A-B of, say, 10 volts, and determine the total current flow. The current flow through each of the 5 resistors are unknowns, and you can set up 5 equations using Kirchoff's circuit laws. Solve for the currents, then find the total current I. The equivalent resistance is 10volts/I.