Simran and stairs

Simran is running up a staircase with N steps, and can hop(jump) either 1 step, 2 steps or 3 steps at a time.You have to count, how many possible ways Simran can run up to the stairs.

Input Format:
Input contains integer N that is number of steps

Output Format:
Output for each integer N the no of possible ways w.

Constraints
1 <= N <= 30

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

int solve(int n) {
  if (n <= 1) return 1;
  if (n == 2) return 2;
  if (n == 3) return 4;
  return solve(n - 1) + solve(n - 2) + solve(n - 3);
}
int main() {
  int n;
  cin >> n;
  cout << solve(n) << endl;
  return 0;
}

References