function mintTokens(address beneficiary, uint256 tokens) internal   {
        require(beneficiary != 0x0);
        uint256 weiAmount;
        if (block.timestamp >= time0 && block.timestamp < time1) weiAmount = tokens.mul(65).div(1000);
        else if (block.timestamp >= time1 && block.timestamp < time2) weiAmount = tokens.mul(70).div(1000);
        else if (block.timestamp >= time2 && block.timestamp < time3) weiAmount = tokens.mul(75).div(1000);
        else if (block.timestamp >= time3 && block.timestamp < time4) weiAmount = tokens.mul(80).div(1000);
        else if (block.timestamp >= time4 && block.timestamp < time5) weiAmount = tokens.mul(85).div(1000);
        else if (block.timestamp >= time5 && block.timestamp < time6) weiAmount = tokens.mul(90).div(1000);
        else if (block.timestamp >= time6 && block.timestamp < time7) weiAmount = tokens.mul(95).div(1000);

        weiRaised = weiRaised.add(weiAmount);
        token.mint(beneficiary, tokens);
        TokenPurchase(msg.sender, beneficiary, weiAmount, tokens, block.timestamp);
    }