#include <iostream>
#include <fstream>

using namespace std;

int main() {
    FILE * in = fopen("kfib.in", "r");
    FILE * out = fopen("kfib.out", "w");
    long k, i;
    fscanf(in, "%ld", &k);
    long long vec[k];
    vec[0] = 0; vec[1] = 1; vec[2] = 1;
    for (i = 4; i <= k; i++) {
            vec[i - 1] = vec[i - 2] + vec[i - 3];
    }
    fprintf(out, "%Ld", vec[k - 1]);

    return 0;
}