#include <string.h>

size_t strcspn(const char *s1, const char *s2) {
	size_t len = 0;
	const char *p;

	while (s1[len]) {
		p = s2;
		while (*p) {
			if (s1[len] == *p++) {
				return len;
			}
		}
		++len;
	}
	return len;
}