#include <stdio.h>
using namespace std;
int main() {
    float f, w;
    scanf("%f", &f);
    if (f <= 15) w = f / 1.5;
    else w = 10 + (f - 15) / 2.5;
    printf("%.2f", w);
    return 0;
}
/**************************************************************
	Problem: 1052
	User: fuhoubin
	Language: C++
	Result: Accepted
	Time:10 ms
	Memory:1144 kb
****************************************************************/