输入n是书的页数，然后返回从1到n中1的出现次数
#include <iostream>
#include <cstdio>
 
using namespace std;
 
int main()
{
    int n;
    scanf("%d", &n);
    int sum = 0;
    int k;
    for(int i = 1; k = n / i;i *= 10)
    {
        sum += k/10 * i;
        int tem = k % 10;
        if(tem > 1)
            sum += i;
        if(tem == 1)
            sum += n - k*i + 1;
    }
    printf("%d\n", sum);
    return 0;
}