1748 수 이어쓰기1

#include <stdio.h>
#include <math.h>
 
int main() {
    long long n;
    scanf("%lld", &n);
 
    long long tenN = 1;
    while (tenN <= n) {
        tenN *= 10;
    }
    tenN /= 10;
 
    long long ten = 1, len = 1, rst = 0;
    while (ten < tenN) {        
        rst += len * (ten * 10 - ten);
        
        len++;
        ten *= 10;
    }
 
    if(n >= ten)
        rst += (n + 1 - ten) * len;
 
    printf("%lld", rst);
}