题解

#include<cstdio>
#include<iostream>
#include<cmath>
using namespace std;
int main(){
int a,b=0,c;
cin>>a;
for(int i=1;i<=a;i++){
c=i;
while(c){
if(c%10==1)b++;
c=c/10;
}
}
cout<<b;
return 0;
}