long long is a standard C++ type, so if you use gcc, you can use this type without any problem. But on Windows, as some old Microsoft C++ compilers don’t support the type long long, you have to use the non-standard type: __int64.

The following example shows how to input and output an __int64 type of variable.

__int64 a;
scanf("%I64d",&a);
printf("%I64d",a);