//1)
#include <stdio.h>

long long int recFact(int a)
{
    if( a < 0 ) return 0;
    else if ( a == 0 ) return 1;
    else return a * recFact( a - 1 );
}

int main(){
    int a;
    scanf("%d", &a);
    long long b = recFact(a);

    printf("%lld", b);

    return 0;
}


/////
//2)
#include <stdio.h>

double recPow(int a, int b)
{
    if (b == 0) return 1;
    if (a == 0) return 0;
    if (b > 0) return a * recPow(a, b-1);
    if (b < 0) return (1.0/recPow(a, -b));
    return 0;
}

int main() {
    int a, b;
    scanf("%d%d", &a, &b);

    double k = recPow(a, b);
    printf("%lf", k);

    return 0;
}

//////////
//3)
#include <stdio.h>

void pr(int c)
{
    if (c == 0) return;

    int n;
    scanf("%d", &n);
    pr(c - 1);
    printf("%d ", n);

}

int main() {
    int a;
    scanf("%d", &a);
    pr(a);
    return 0;
}

///////
//4)
#include <stdio.h>
#include<stdlib.h>
#include<string.h>
void recDecToBin(int n, char* result)
{
    if (n < 0) return;

    int del = n%2;
    n /= 2;
    if (n == 0) {
        if (del == 1)
            strcat(result, "1");
        else strcat(result, "0");
    return;
    }
    recDecToBin(n, result);

    if (del == 1)
        strcat(result, "1");
    else strcat(result, "0");
}

int main(){
    int n;
    // char result[30] = "";
    char *result = (char*) malloc (30 * sizeof(char));
    scanf("%d", &n);
    // вызов функции recDecToBin
    recDecToBin(n, result);
    // puts(result);
    printf("%s", result);
    return 0;
}


////
//5)
#include <stdio.h>

static int count = 0;
long long int recSum(long long int arr[])
{
    int i = count;
    count++;

    if (count == 100) return arr[i];
    return arr[i] + recSum(arr);
}

int main() {
    long long int arr[100];
    for (int i = 0; i < 100; i++) scanf("%lld", &arr[i]);

    long long int k = recSum(arr);

    printf("%lld", k);

    return 0;
}


///////
//6)
#include <stdio.h>
#include <stdlib.h>
int n, m, k = 0;
int labirint(int **a, int x, int y){
    if (a[x][y] == 1) return 0;
    a[x][y] = 1;
    if (x == n-1 && y == m-1) k = 1;
    if (x-1>=0) labirint(a, x-1, y);
    if (y-1>=0) labirint(a, x, y-1);
    if (y+1<m) labirint(a, x, y+1);
    if (x+1<n) labirint(a, x+1, y);
    if (k == 1) return 1;
    else return 0;
}

int main() {
    scanf("%d%d", &n, &m);
    int **a = malloc(n * sizeof(int*));
    for (int i = 0; i < n; i++){
        a[i] = malloc(m * sizeof(int));
        for(int j = 0; j < m; j++){
            scanf("%d", &a[i][j]);
        }
    }
    if(labirint(a, 0, 0)) printf("exists");
    else printf("doesn't exist");
    return 0;
}


///////
7)
#include <stdio.h>
#include <stdlib.h>
int h, w;

int count(int* * a, int x, int y, int tmp){
    if(a[y][x] == 0)return tmp;
    a[y][x] = 0;
    tmp++;

    if (x-1>=0) tmp = count(a, x-1, y, tmp);
    if (y-1>=0) tmp = count(a, x, y-1, tmp);
    if (y+1<h) tmp = count(a, x, y+1, tmp);
    if (x+1<w) tmp = count(a, x+1, y, tmp);
    return tmp;
}


int main(){
    int max = 0;
    scanf("%d%d", &h, &w);
    int* * arr = malloc(h* sizeof(int *));
    for(int i = 0; i < h; i++){
        arr[i] = malloc(w * sizeof(int));
        for(int j = 0; j < w; j++){
            scanf("%d", &arr[i][j]);
        }
    }

    for(int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {

            if (arr[i][j] == 1) {
                int tmp = 0;
                tmp = count(arr, j, i, tmp);
                if (tmp>max)max = tmp;
            }
        }

    }
    printf("%d", max);
    return 0;
}