#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <limits.h>
#include <stdbool.h>

long int countArray(int n, int k, int x) {
    // Return the number of ways to fill in the array.
    long int answer=0,m;
    for(int i=2;i<n;i++)
        answer=answer+(n-i);
    return answer;
}
int main() {
    int n; 
    int k; 
    int x; 
    scanf("%i %i %i", &n, &k, &x);
    long int answer = countArray(n, k, x);
    printf("%ld\n", answer);
    return 0;
}