#include <stdio.h>
long long count(long long n,int k) {
    long long cnt=0;
    while(n>=k) {
        cnt+=n/k;
        //k*=k;
        n/=k;
    }
    return cnt;
}

long long min(long long a,long long b){
    return a<b ? a:b;
}
int main() {
    int n,m;
    int cntn,cntm;
    scanf("%d %d",&n, &m);
    long long five =count(n,5)-count(m,5)-count(n-m,5);
    long long two =count(n,2)-count(m,2)-count(n-m,2);
    printf("%lld",min(two,five));
    return 0;
}