#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    int dp[n+1];
    if (n == 1) {
        cout << 1;
        return 0;
    }
    else if (n == 2) {
        cout << 2;
        return 0;
    }
    else if (n == 3) {
        cout << 4;
        return 0;
    }

    else{
        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 4;
        for (int i = 4;i <= n;i++) {
            dp[i] = (dp[i-1]+dp[i-2]+dp[i-3])%1000;
        }
     }
    cout << dp[n];
    return 0;
}