#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float c;
    cin>>n;
    c=(n-2)*180;
    printf("%.1f",c/n);
	
	
}
/**************************************************************
	Problem: 1317
	User: lvrenxiang
	Language: C++
	Result: Accepted
	Time:13 ms
	Memory:2072 kb
****************************************************************/