#include<bits/stdc++.h>
using namespace std;
int main(){
	int n;
	float a,b=3;
	scanf("%d",&n);
	a=(n-2)*180/b;
	printf("%.1f",a);

}

/**************************************************************
	Problem: 1317
	User: zhengzihao3
	Language: C++
	Result: Wrong Answer
****************************************************************/