n的阶乘的位数

#include <stdio.h>
#include <math.h>
#define PI 3.1415926
int main() {
	int n , a;
	while(~scanf("%d",&n)) {
		a = (int) ((0.5*log(2*PI*n) + n*log(n) - n) / log(10));
		printf("%d\n",a+1);
	}
	return 0;
}