resp 2012 - 2-2

#include <cstdio>
#define N 1111111

using namespace std;

int a,b,n,m,phi[N];
bool bs[N];
long long ans;

long long getsum(int x){
    return x*1ll*(x+1)/2;
}

void calc_phi(int n){
    for (int i=1;i<=n;i++) phi[i]=i;
    for (int i=2;i<=n;i++){
        if (bs[i]) continue;
        for (int j=i;j<=n;j+=i){
            bs[j]=1;
            phi[j]-=phi[j]/i;
        }
    }
}

void solve(int n,int m){
    int k=n<?m;
    for (int i=1;i<=k;i++) ans+=phi[i]*1ll*(n/i)*(m/i);
}

int main(){
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);
    scanf("%d%d%d%d",&n,&m,&b,&a);
    calc_phi(n<?m);
    solve(a-1,b-1);
    solve(a-1,m-b);
    solve(n-a,b-1);
    solve(n-a,m-b);
    ans+=getsum(a-1)+getsum(b-1)+getsum(n-a)+getsum(m-b);
    printf("%I64d\n",ans);
    return 0;
}