func: function _ethereumToTokens(uint256 _ethereum) internal view returns(uint256) {
          uint256 _tokenPriceInitial = initialTokenPrice * 1e18;
          uint256 tokenAmount = 
           (
              (
                  SafeMath.sub(
                      (_sqrt
                          (
                              (_tokenPriceInitial**2)
                              +
                              (2*(tokenIncrement * 1e18)*(_ethereum * 1e18))
                              +
                              (((tokenIncrement)**2)*(totalSupply**2))
                              +
                              (2*(tokenIncrement)*_tokenPriceInitial*totalSupply)
                          )
                      ), _tokenPriceInitial
                  )
              )/(tokenIncrement)
          )-(totalSupply)
          ;
          return tokenAmount;
      }