Sum of first N numbers

sumOf_N_Numbers.cpp 
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#include <bits/stdc++.h>
using namespace std;

int sumOf_N_Numbers(int n){
    int sum=0;
    if(n==0)
        return 0;
    sum = n + sumOf_N_Numbers(n-1);
    return sum;
}

int main() {
    int n;
    cin >> n;
    cout << sumOf_N_Numbers(n);
    return 0;
}
Output 
5
15