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| #include <cstdio>
using namespace std;
template <class Type>
void read(Type &x)
{
char c;
bool flag = false;
while ((c = getchar()) < '0' || c > '9')
c == '-' && (flag = true);
x = c - '0';
while ((c = getchar()) >= '0' && c <= '9')
x = (x << 3) + (x << 1) + c - '0';
flag && (x = ~x + 1);
}
template <class Type>
void write(Type x)
{
x < 0 && (putchar('-'), x = ~x + 1);
x > 9 && (write(x / 10), 0);
putchar(x % 10 + '0');
}
const int N = 1e3 + 10;
int n, m;
double f[N][N][3];
double dfs (int x, int y, int op)
{
if (f[x][y][op] > 1e-10)
return f[x][y][op];
if (!x || y < 0)
return 0;
if (op == 0)
return f[x][y][op] = (double)x / (x + y) + (double)y / (x + y) * dfs(x, y - 1, 1);
else if (op == 1)
return f[x][y][op] = (double)y / (x + y) * dfs(x, y - 1, 2);
return f[x][y][op] = (double)x / (x + y) * dfs(x - 1, y, 0) + (double)y / (x + y) * dfs(x, y - 1, 0);
}
int main ()
{
read(n), read(m);
printf("%.12lf", dfs(n, m, 0));
return 0;
}
|