#include<stdio.h>
#include<stdlib.h>
using namespace std;
int sub2(int i);

int even_sum(int n);
int x;
/*
int even_sum(int n)
{

//int x=0;
while (n>=0)
{


//printf("test");
return 2+x+ even_sum(n-1);
//return (even_sum(sub2(n)));

}
}
*/
int sub2(int i)
{
    i=i--;
    return i;
}


int even_sum(int n)
{


if (n==0)
{
         return n;
}


else
{
    x=x+2;

//printf("test");
return  (even_sum(sub2(n)));

}
}



int main()
{
        int sol;
    int n;
    printf("enter numbers \n");
    scanf("%d", &n);
    sol= even_sum(n);
    printf("the sum is: %d \n", sol);

/*
    FILE *inp, *outp;
    int sol;
    int n;

    inp = fopen("D:datause.dat", "r");
    outp= fopen("D:dataout.out", "w");
    fscanf(inp, "%d", &n);
    //n=n*2;
    sol=even_sum(n);
    fprintf(outp, "the integer input is %.2d.\n The sum of all the even numbers from 2 to %.2d. is %d", n, n, sol);
*/

    system("pause");

}