The approximate number obtained by rounding the number 57409236 to 100,000 digits is a, the approximate number obtained by rounding to the thousandth digit is b, and the approximate number obtained by rounding to the millionth digit is c, then what is the value of c+ab.
把数57409236四舍五入精确到十万位得到的近似数为a，精确到千位得到的近似数为b，在百万位四舍五入得到的近似数为c，那么c+a-b的值是多少．
<gadget id="calculator">57_400_000 - 57_409_000</gadget>
<output>-9_000</output>

<gadget id="calculator">57_000_000 + (-9_000)</gadget>
<output>56_991_000</output>

<result>56_991_000</result>