#include<iostream>
using namespace std;
class calc{
    public:
    float add(float a,float b){
        return a+b;
    }
    float sub(float a, float b){
        return a-b;
    }
    float mul(float a, float b){
        return a*b;
    }
    float div(float a, float b){
        return a/b;
    }
};
int main(){
    calc obj;
    int t;
    cin>>t;
    float a,b;
    if(t==1){
        cout<<obj.sub(a,b);
        
    }
    else if(t==2){
        cout<<obj.sub(a,b);
        
    }
    else if(t==3){
        cout<<obj.mul(a,b);
        
    }
    else if(t==4){
        if(b==0){
            cout<<"division by zero"<<endl;
        }
        else{
            cout<<obj.div(a,b);
        }
        
    }
    else{
        cout<<"Invalid input";
    }
    return o;
}