C++ :

#include<bits/stdc++.h>
using namespace std;
int q,a,z,w,s,x,e,d,c,r,f,v,t,g,b,y,h,n,u,j,m,i,k,o,l,p;
int main(){
cin>>n;
while(n!=0){
s=n%10;
n=n/10;
if(s==1){
c++;
}
}
cout<<c;
return 0;
}