function mintTokensToEralyInvestors() onlyOwner {
    require(!earlyInvestorsMintedTokens);
    for(uint i  = 0; i < presale.totalInvestors(); i++) {
      address investorAddress = presale.investors(i);
      uint invested = presale.balanceOf(investorAddress);
      uint tokens = invested.mul(1 ether).div(price);
      uint bonusTokens = tokens.mul(earlyInvestorsBonus).div(percentRate);
      uint tokensWithBonus = tokens.add(bonusTokens);
      token.mint(this, tokensWithBonus);
      token.transfer(investorAddress, tokensWithBonus);
    }
    earlyInvestorsMintedTokens = true;
  }