#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float a;
	cin>>n;
	a=(n-2)*180/n;
    printf("%.1f",a);
	return 0;
}

/**************************************************************
	Problem: 1317
	User: zhenghaoxuan
	Language: C++
	Result: Wrong Answer
****************************************************************/