BZOJ 3000: Big Number|斯特林公式

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<queue>
#include<vector>
#include<set>
#include<map>
#include<algorithm>
#include<iostream>
#define N 220050
#define M 4000001
#define e exp(1.0)
#define pi acos(-1.0)
using namespace std;
int sc()
{
int i=0,f=1; char c=getchar();
while(c>'9'||c<'0'){if(c=='-')f=-1;c=getchar();}
while(c>='0'&&c<='9')i=i*10+c-'0',c=getchar();
return i*f;
}
int n,k;
int main()
{
while(~scanf("%d%d",&n,&k))
{
double x=0;
if(n<=100)
{
for(int i=2;i<=n;i++)
x+=log(i);
x/=log(k);
printf("%lld\n",(long long)floor(x)+1ll);
}
else
{
x=log(2*pi*n)/log(k)/2+n*log(n/e)/log(k);
printf("%lld\n",(long long)floor(x)+1ll);
}
}
return 0;
}