#include <stdio.h>

int tri(int n) {
    if (n <= 1) return 0;
    if (n == 2) return 1;
    return tri(n - 1) + tri(n - 2) + tri(n - 3);
}

int main(void) {
    int n = 7;
    printf("数列Tnについて, n=%dのときの値は%d\n", n, tri(n));
    return 0;
}