#include <stdio.h>
int main(void){
    int x;
    int ans;
    
    scanf("%d", &x);
    if (x == 2)
        ans = 2;
    else {
        ans = 5 * x - 10;
        if (x%2 == 0)
            ans -= 6;
    }
    printf("%d\n", ans);
    return 0;
}