#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    char buffer[BUFSIZ];
    if (setvbuf(stdin, buffer, _IOFBF, BUFSIZ) != 0) { // here
        printf("an error occured.n");
        exit(1);
    }
    int number;
    scanf("%d", &number);
    printf("number : %dn", number);
    return 0;
}

3
number : 3