#include<bits/stdc++.h> using namespace std; #define LL long long const int N = 1e5 + 10; const int INF = 0x3f3f3f3f; int main() { string a; cin >> a; int len = a.size(); while(len > 1) { int sum =0; for(int i = 0 ; i < len ; i++) sum += a[i] - 48; a = to_string(sum); len = a.size(); } cout << a << endl; return 0; }