#include "bits/stdc++.h"
#define MOD 1000000007
#define inf 0x3f3f3f3f
#define pi acos(-1.0)
#define ri register int
#define Max(x, y) (((x) > (y)) ? (x) : (y))
#define Min(x, y) (((x) < (y)) ? (x) : (y))
#define Abs(x) ((x) < 0 ? (-(x)) : (x))
#define int long long
const int maxn = 1e3 + 10;
inline int read()
{
    int f = 1, r = 0;
    char c = getchar();
    while (!isdigit(c)) {
        if (c == '-') {
            f = -1;
        }
        c = getchar();
    }
    while (isdigit(c)) {
        r = 10 * r + c - '0';
        c = getchar();
    }
    return f * r;
}
inline void write(int x)
{
    if (x < 0)
        putchar('-'), x = -x;
    if (x > 9)
        write(x / 10);
    putchar(x % 10 + '0');
}
inline void writesp(int x) { write(x), putchar(' '); }
inline void writeln(int x) { write(x), puts(""); }
int N;
char str[105];
signed main()
{
    N = read();
    scanf("%s", str + 1);
    int x = 0, ans = 0;
    for (ri i = 1; i <= N; ++i) {
        if (str[i] == 'I') {
            x++;
        } else {
            x--;
        }
        ans = Max(ans, x);
    }
    writeln(ans);
    return 0;
}