C++ :

#include <cstdio>
#include <algorithm>
using namespace std;
/* 把两串开枪时刻全部倒进数组，排序去重计个数。2S <= 200000。 */
static long long t[200005];
int main(){
    long long S, t1, t2;
    if(scanf("%lld %lld %lld", &S, &t1, &t2) != 3) return 0;
    int k = 0;
    for(long long i = 0; i < S; i++){
        t[k++] = 1 + i * t1;
        t[k++] = 1 + i * t2;
    }
    sort(t, t + k);
    long long ans = 0;
    for(int i = 0; i < k; i++) if(i == 0 || t[i] != t[i - 1]) ans++;
    printf("%lld\n", ans);
    return 0;
}