#include <iostream> using namespace std; int count1(int n){ if(n == 0){ return 0; } if(n == 1){ return 1; } int countof1innm1 = count1(n-1); int countinn = 0; while(n !=0){ int rem = n%10; if(rem ==1){ countinn++; } n = n/10; } return countinn + countof1innm1; } int main() { int n; cin>>n; cout<<count1(n); }