#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll n,ans,a,b,c,dp[2001],A,B,d,ord[2001];
int main(void){
    cin>>a>>b>>c>>n;
    a%=10,b%=10,c%=10;
    A=100*a+10*b+c;
    memset(dp,-1,sizeof(dp));
    //dp[0]=a,dp[1]=b,dp[2]=c;
    ord[0]=a,ord[1]=b,ord[2]=c;
    for(int i=3;i<2000;i++){
        d=(a+b+c)%10;
        a=b;
        b=c;
        c=d;
        if(dp[100*a+10*b+c]!=-1){B=i,A=dp[100*a+10*b+c];break;}
        else{
            dp[100*a+10*b+c]=i;
            ord[i]=d;
        }
    }
    //cout<<A<<" "<<B<<endl;
    if(n<=A)cout<<dp[n-1]<<endl;
    else{
        n-=A+1;
        n%=B-A;
        //cout<<n+A<<endl;
        cout<<ord[n+A]<<endl;
    }
}