#include <stdio.h>


int sum_natural(int);

int sum_natural(int n){
    if (n==1){
        return 1;
    }
    //sum_natural(n)=1+2+3+4+5+...n-1+n;
    //sum_natural(n)=sum(n-1)+n;
    return sum_natural(n-1)+n;

}
int main() {
    printf("the sum of first five natural numbers is %d",sum_natural(5));
    
    return 0;
}