C :

#include<stdio.h>
 
/**
 * 更相减损
 * @param a
 * @param b
 * @return
 */
int gcd(int a, int b){
    if (a > b) {
        return gcd(a - b, b);
    }
    if (b > a) {
        return gcd(a, b - a);
    }
    return a;
}
 
int main() {
    int a, b;
    int k = scanf("%d,%d", &a, &b);
    if (k != 2 || a <= 0 || b <= 0) {
        printf("Input error!\n");
        return 0;
    }
    printf("%d\n", gcd(a, b));
    return 0;
}