#include<bits/stdc++.h>
using namespace std;
int main(){
    int n;
    float a;
    scanf("%d",&n);
    a=(n-2)*180.0/n*1.0;
    printf("%.1f",a);
}
/**************************************************************
	Problem: 1317
	User: zhangyilei
	Language: C++
	Result: Accepted
	Time:12 ms
	Memory:2076 kb
****************************************************************/