/*
#include <stdio.h>
#include <stdlib.h>
int main()
{
printf("Hello world!\n");
return 0;
}
*/
/*
#include <stdio.h>
int f(int n)
{
if(n==0||n==1)
{
return 2;
}
}
int main()
{
int n;
scanf ("%d",&n);
printf ("%d",f(n));
}
/*
1: 5
2: 10
3: 15
4: 20
...
1+2: 5+10+(-3) = 12
1+2+3: 5+10+15+(-3)+(-5) = 30-8 = 22
1+2+3+4: 5+10+15+20+(-3)+(-5)+(-7) = 50-15 = 35
1+2+3+4+5: 5+10+15+20+25+(-3)+(-5)+(-7)+(-9) = 75-24 = 51
10 , 13 , 16
% -3: -2 -2 + 1
% -5: -3 -3 + 1