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