C++ :

#include<bits/stdc++.h>
using namespace std;
int n,s;
int main()
{
	cin>>n;
	for(int i=1;i<=n;i+=2)
		s+=i;
	cout<<"s="<<s;	
	return 0;
}

Pascal :

var n,i,s:integer;
begin
readln(n);
for i:=1 to n do
  if i mod 2=1 then s:=s+i;
 writeln('s=',s);
end.