#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,ni;
    float jiao;
    cin>>n;
    jiao=(n-2)*180.0/n;
    printf("%.1f",jiao);
}
/**************************************************************
	Problem: 1317
	User: huanglingkai
	Language: C++
	Result: Accepted
	Time:11 ms
	Memory:2072 kb
****************************************************************/