求n！(十进制)的位数

#include <iostream>
#include <cmath>
using namespace std;

int ()
{
    int N;
    while(scanf("%d", &N) != EOF){
        double sum = 0.0;
        for(int i = 2; i <= N; i++)
            sum += log10(i);
        printf("%dn", (int)sum + 1);
    }
    return 0;
}