#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main(void){
    int a,b,ans;
    cin>>a;
    if(a<=9){
        cout<<a<<endl;
    }else if(a%2==1){
        ans=((a-10)/2+10)%10;
        cout<<ans<<endl;
    }else{
        ans=((a-10)/2+10)/10;
        cout<<ans<<endl;
    }

}