#include<bits/stdc++.h>
using namespace std;
using Int=long long;
using Real=long double;
template<class T,class S>inline bool chmin(T&A,S B){return(A>B?A=B,1:0);}
template<class T,class S>inline bool chmax(T&A,S B){return(A<B?A=B,1:0);}
#define REP(i,n)for(int i=0;i<(n);++i)
#define REP1(i,n)for(int i=1;i<=(n);++i)
#define ALL(x)begin(x),end(x)
#define drop(x){cout<<(x)<<'\n';return;}
int N;
void sol()
{
	cin>>N;
	REP(i,99)
	{
		int nN=0;
		while(N)nN+=N%10,N/=10;
		N=nN;
	}
	cout<<N<<"\n";
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	cout<<fixed<<setprecision(16);
	int T=1;
	//cin>>T;
	while(T--)sol();
}