The aim of the paper is to study of the mean field games with common noise. The MFG limit is specified by a single quasi-linear deterministic infinite-dimensional partial differential second order backward equation. We show that any its solution provides an 1/N-Nash equilibrium for the initial game of N agents. Our basic approach is based on interpreting the common noise as a kind of binary interaction of agents and then reducing the problem to the sensitivity analysis for McKean-Vlasov SPDE.