#include <cstdio>
int num = 0;
int Find(int currLen, int maxLen, int all) {
	if (currLen > maxLen || num > all) {
		return 0;
	}
	if (num == all && currLen <= maxLen) {
		return 1;
	} 
	num++;
	return Find(currLen, maxLen, all) + Find(currLen + 1, maxLen, all);
}
int main() {
	int n, a, b;
	scanf("%d%d%d", &n, &a, &b);
	if (a > b || b - a > n) {
		printf("0\n");
	} else {
		printf("%d\n", Find(a, b, n));
	}
	return 0;
}