View Compilation Error

0_0_6273664_28856\Main.java:6: incompatible types
found   : int
required: java.math.BigInteger
         static BigInteger a=1;
                             ^
0_0_6273664_28856\Main.java:12: incompatible types
found   : int
required: java.math.BigInteger
			for(i=1;i<=b;i++)a*=i;
			      ^
0_0_6273664_28856\Main.java:12: operator <= cannot be applied to java.math.BigInteger,java.math.BigInteger
			for(i=1;i<=b;i++)a*=i;
			         ^
0_0_6273664_28856\Main.java:12: operator ++ cannot be applied to java.math.BigInteger
			for(i=1;i<=b;i++)a*=i;
			              ^
0_0_6273664_28856\Main.java:12: operator * cannot be applied to java.math.BigInteger,java.math.BigInteger
			for(i=1;i<=b;i++)a*=i;
			                  ^
5 errors