include

int main() { int n, a, b, c;

scanf("%d", &n);
scanf("%d %d %d", &a, &b, &c);

int last_three[3];
last_three[0] = a;
last_three[1] = b;
last_three[2] = c;

int sum = last_three[0] + last_three[1] + last_three[2];

if (n==3) {
    printf("%d", c);
}

else if (n==2){
    printf("%d", b);
}

else if (n==1){
    printf("%d", a);
}

else {

for (int i = 3; i < n-1; i++) {
    last_three[0] = last_three[1];
    last_three[1] = last_three[2];
    last_three[2] = sum;

    sum = last_three[0] + last_three[1] + last_three[2];
}

printf("%d\n", sum);
}

return 0;

}